The Christmas Invasion (TV story)

The Christmas Invasion was the 2005 Christmas Special of Doctor Who.

It was the show's first Christmas special since its revival and the first Christmas special starring Tennant as the Doctor.

It was the first episode of Doctor Who to premiere on Christmas Day since "The Feast of Steven", the seventh part of 1966 twelve-part serial The Daleks' Master Plan. However, unlike that episode, The Christmas Invasion was specially commissioned by BBC One to be transmitted outside the programme's normal broadcasting season. It was thus the first in the modern tradition of the "Christmas special", and its sixty-minute running time made it then the longest episode yet produced by BBC Wales.

Narratively, it continued the story of Harriet Jones, started the Torchwood story arc and involved UNIT in its first major appearance in the new series.

More importantly, it was the first full story to feature the Tenth Doctor, played by David Tennant. Its initial pre-titles sequence on the Powell Estate was later used to "bookend" the closing scenes of The End of Time. Its setting was the first and last place on Earth the Tenth Doctor saw.

To coincide with this release, three short stories were released on the U.N.I.T. website. The first was Alien Life, part of the UNIT Press Briefings mini-series, which was set directly in the aftermath of the Sycorax invasion, where UNIT confirms that aliens exist, and the second and third, Guinevere One and Project Rooftop, part of the Operations Board mini-series, was set during and after The Christmas Invasion, respectively, depicting events of the television story from UNIT's perspective.

Synopsis
It's Christmas Eve and high above London, the alien Sycorax are holding the Earth for ransom. The Tenth Doctor must recover from his regeneration in time to save the human race from slavery.

Plot
It is Christmas Eve on Earth. As Jackie prepares presents and Mickey works in the local garage, both of them hear the distinctive sound of the TARDIS' engines. Rushing out into the street of the Powell Estate, they see the TARDIS blink into existence above them, ricochet off a few buildings and a post van, then come to a crashing halt. A freshly-regenerated Doctor stumbles out of the police box doors, greets the two of them by name and wishes them a merry Christmas before collapsing. Rose follows and, in response to Jackie and Mickey's questions, identifies him as the Doctor.

They bring the Doctor to Jackie's flat and dress him in pyjamas belonging to Howard, Jackie's current beau, who has the habit of keeping pieces of fruit in his pocket for snacks. While Rose discusses the Doctor's change of appearance and the fact he has two hearts with Jackie, they do not see a wisp of regeneration energy emerging from the Doctor's mouth, which then floats off into space. On television, Prime Minister Harriet Jones and project director Daniel Llewellyn give a press conference about the Guinevere One space probe, which is about to land on Mars. In space, however, the probe is swallowed up by an rock-like spaceship.

That evening, Rose and Mickey go Christmas shopping but are attacked by a group of masked Santas armed with lethal musical instruments. Managing to escape when the tuba mortar brings a giant Christmas tree down on the Santas, Rose realises that their attackers are after the Doctor. She and Mickey rush home in a taxi. When they reach the flat, Rose notices an unfamiliar Christmas tree in the sitting room, which Jackie says was delivered to the door. As they deduce that none of them purchased the tree, it suddenly comes to life, whirling around with razor-sharp branches while playing a cheerful rendition of "Jingle Bells" as it tries to slice them all to ribbons. The three retreat to the bedroom with the tree in hot pursuit. As Jackie laments the indignity of being "killed by a Christmas tree", Rose places the sonic screwdriver in the still-comatose Doctor's hand and begs him to help her. Reacting instinctively, the Doctor rises just as the tree bursts through the door and disintegrates it with the screwdriver.

He then strides outside the flat to see who was remotely controlling the tree. From ground level, the Santas stare up at the Doctor, but transmat away when he threateningly points the sonic screwdriver at them. The Doctor calls them "pilot fish" before collapsing in pain: he is still regenerating, and the energy leaking from him has attracted the "pilot fish"'s attention. He tells them he is having a neural implosion because they woke him up too soon, but Jackie keeps interrupting with a stream of increasingly unhelpful suggestions until the Doctor tells her to shut up. He grips Rose, warning her that something bigger is coming, then loses consciousness again.

The first signal from Guinevere One arrives on television: a snarling alien face, which is soon broadcast all over the world. Llewellyn is escorted by Major Blake to the Tower of London, which houses an underground facility run by the United Nations Intelligence Taskforce. There, he meets the Prime Minister and her aide, Alex, who tells him that they're putting out a temporary cover story that students in masks hacked into the television signal. Llewellyn is shaken to realise that extraterrestrial life does indeed exist and that both the British government and the United Nations are aware of this. A technician, Sally Jacobs, explains that the signal did not come from Mars but 5000 miles above the planet's surface, which means that there is a ship, and it is moving rapidly towards Earth.

As Rose and Mickey use his laptop to access the UNIT website and monitor their readings, the aliens send another signal to Earth. They speak in a language that Rose does not understand; normally, the TARDIS would translate it for her, but it seems that with the Doctor unconscious, that function is not working. Rose examines the bedridden Doctor and finds one of his hearts has stopped, meaning he is too injured to be of use and may die if they attempt to wake him again. Back at UNIT, Blake orders the use of translation software. With no sign of the Doctor, Jones asks Blake about Torchwood. She knows that she is not supposed to know about them – not even the United Nations knows — but she wants them to be ready.

The software translates the message: the aliens are called the Sycorax, and they are claiming the planet as their own, demanding surrender or "they" will die. Their word for "human" also appears to be similar to that of "cattle", temporarily baffling UNIT. Jones declines to surrender, replying to the Sycorax with a warning that the planet is armed. As dawn rises over London, the Sycorax enact their first move. With a wave of the leader's hand, blue energy sweeps over a third of the world's population, mesmerising them. The mind-controlled people, Sally Jacobs amongst them, then climb to the highest spots they can find, primarily the roofs of buildings, and stand at the edge, all of them poised to jump.

Checking the UNIT staff's medical records, Llewellyn discovers that all the affected people have A+ blood. The Sycorax found the sample of A+ blood that was sent with other materials on Guinevere One to identify the human race in case of alien contact, and are somehow using that as a control mechanism. Desperate now, Jones gives an emergency broadcast on television, informing the public that the Queen's Christmas speech has been cancelled as the Royal Family are "on the roof", and pleads for the Doctor's help if he is out there. Driven to despair by the Doctor's comatose state, Rose breaks down in tears in Jackie's arms.

Just then, the shockwave of the Sycorax ship entering the atmosphere shatters windows all over the city; the gigantic craft takes position above the Houses of Parliament and an under-reconstruction Big Ben as the frightened population watch. Rose, not knowing what else to do, asks Mickey and Jackie to help her move the Doctor to the safety of the TARDIS. Jackie gathers food and other supplies, including a thermos flask of tea.

The Sycorax teleport Jones, Alex, Blake and Llewellyn up to their ship, where the Sycorax leader removes his helmet, revealing a skinless face surrounded by a mantle of bone. His hand hovering over a large glowing button, he demands immediate surrender, or he will order the mind-controlled humans to jump. Llewellyn tries to reason with the Sycorax but is reduced to a pile of bones by the leader's energy whip, as is Blake when he protests. The choice is left to Jones; half of the world will be sold into slavery or a third will die.

As Rose and Mickey move the Doctor into the TARDIS console room, Jackie goes back to get more supplies. Rose, having apparently given up, broods by the console as Mickey tries to use the scanner to tune into what is happening, but the time machine's advanced technology is detected by the Sycorax. Outside, Jackie watches helplessly as the TARDIS is transmatted up. Not realising that they are aboard the Sycorax ship, Rose steps out of the TARDIS and screams when she sees the aliens. Mickey rushes out after her, dropping the flask of tea, which spills and starts dripping through the grilles at the base of the console next to the Doctor's unconscious form. The Doctor breathes in the subsequent fumes as the tea sparks against various components.

Reunited with Harriet Jones, Rose tries to bluff the Sycorax by citing various things and races she has encountered on her travels, commanding them to leave, but is answered with laughter. The Sycorax leader taunts her attempts to pass off second-hand knowledge as authority... but as he gloats, his alien words start being replaced with English. Rose realises that the TARDIS translation ability is working again, and since the Doctor must be conscious for it to be active, that can mean only one thing: the Doctor is awake. On cue, the Doctor emerges from the TARDIS in Howard's dressing gown, smiling as he says, "Did you miss me?"

Easily deactivating the Sycorax leader's energy whip and breaking his staff, the Doctor bluntly tells the alien to wait while he gets more important things out of the way; namely, getting reacquainted with his friends. Disappointed at not being "ginger" (red-haired), and somewhat annoyed at Rose's speed in giving up on him, he tells them that all he needed was a "good cup of tea; a superheated infusion of free radicals and tannin. Just the thing for healing the synapses." As the Sycorax leader demands to know who he is, the Doctor blithely strides across the ship's floor, nattering on cheerfully and still working out what his personality is like in this new incarnation. He walks up to the glowing button, discovers that it is powered by A-positive human blood, and quickly deduces that the Sycorax are using blood control — they're controlling all the humans with A-positive blood. The Doctor tells the leader that in his unstable state, when he sees a large glowing button he just cannot help himself — and to everyone's shock, he pushes it.

However, instead of sending the possessed crowds on Earth to their deaths, it simply releases them from the Sycorax control. The Doctor explains that blood control is like hypnosis: "you can hypnotise someone to cluck like a chicken or sing like Elvis, but you can't hypnotise them to death. Survival instinct's too strong." The Sycorax were bluffing, and the Doctor called them on it. The leader says that they can still conquer Earth by force with an armada, but the Doctor demands that the humans be left alone (quoting part of "The Circle of Life" from The Lion King in the process), challenging the leader to single combat for the planet.

The Doctor goads the leader into the fight by insulting him in his native Sycoraxic. The swordfight ranges from inside the ship to its exterior; in the midst of it, the leader cuts the Doctor's hand off, and it falls to the city below along with his sword. The leader assumes the Doctor will yield as he's been "disarmed". But while his friends are horrified, the Doctor is calm; he notes that he is still within the first fifteen hours of his regeneration cycle. Grinning, he explains that there's enough leftover energy after the change to rectify any anomalies or missing bits; and his hand regrows.

Grabbing a new sword, the Doctor notes "This new hand, it's a fightin' hand!" and reengages the leader in battle, ultimately winning the duel. The Doctor pins the leader to the edge of the ship with his sword, commanding him to leave the planet and never return in exchange for sparing his life. As the Sycorax leader appears to yield and the Doctor walks back to celebrate his victory with Rose, he attempts a final attack whilst the Doctor's back is turned. In response, the Doctor calmly bounces a satsuma he finds in Howard's dressing gown off a control button, opening a section of the ship's wing beneath the leader, sending the alien plunging to his death. With a now-grim expression, the Doctor declares he is a man who doesn't give second chances.

The Doctor sends the other Sycorax on their way with a reminder that the planet Earth is defended, and he and his human friends are transmatted back to London to reunite with Jackie. Jones asks the Doctor if there are more aliens out there, and he confirms that there are thousands; the human race is being noticed more and more and it is something they will have to get used to. As Jones ponders this, visibly troubled, Alex receives a telephone call and quietly informs Jones that Torchwood is ready. Jones appears reluctant, but nevertheless gives the order to fire. The Doctor and his friends watch in shock as five green beams converge into one over London, and the resulting energy burst destroys the Sycorax ship as it heads into space. The Doctor is furious with Jones, but the Prime Minister tries to justify the use of the weapon (engineered from a crashed spaceship ten years previously) as defending the planet. She tells him how Llewellyn and Blake were mercilessly killed in front of her while the Doctor was asleep, making her realise he cannot be there all the time. The Doctor bitterly retorts he should have warned the Sycorax to run, as the real monsters, the humans, are coming. When Jones asks if she should consider the Doctor another alien enemy, the Doctor warns her that he can bring down her government with just six words, which he whispers into Alex's ear: "Don't you think she looks tired?" Alex gives Jones a startled look, and she demands to know what the Doctor just said, growing frantic in her attempts. Everyone else leaves without a word, and Jones can only apologise quietly.

While the Doctor looks through the TARDIS wardrobe for a new outfit to suit his new incarnation, Jackie, Mickey and Rose serve Christmas dinner in the flat. The Doctor joins them to celebrate, having finally settling on a brown pinstripe suit and a long brown coat. On television, Harriet Jones is seen fending off rumours about her ill-health and a pending vote of no confidence in the House of Commons. Outside, what looks like snow is falling over London, accompanied by shooting stars, but the Doctor points out that it is, in fact, ash — the remains of the Sycorax spaceship breaking up in the atmosphere. It is a new start for Earth, however; with so many people seeing the Sycorax ship, there is no covering up the existence of aliens this time.

But there are new worlds to see and explore. With a now-trusting Rose by his side and eager to continue their travels, the Doctor looks up into the sky to choose a star for their next destination, assuring her that it will be, in the words of his previous incarnation, "fantastic".

Cast

 * The Doctor - David Tennant
 * Rose Tyler - Billie Piper
 * Jackie Tyler - Camille Coduri
 * Mickey Smith - Noel Clarke
 * Harriet Jones - Penelope Wilton
 * Danny Llewellyn - Daniel Evans
 * Alex - Adam Garcia
 * Sycorax Leader - Sean Gilder
 * Major Blake - Chu Omambala
 * Sally - Anita Briem
 * Alan - Marvyn Williams
 * Sandra - Sian McDowall
 * Jason - Paul Anderson
 * Mum - Cathy Murphy
 * Policeman - Seán Carlsen
 * Newsreader 1 - Jason Mohammed
 * Newsreader 2 - Sagar Arya
 * Newsreader 3 - Lachele Carl

Uncredited cast

 * Jeffrey Baxter - Ian Hilditch

The Doctor

 * The Doctor has recently regenerated from his ninth incarnation.
 * The leader of the Sycorax slices off the Doctor's hand. However, the Doctor regenerates the hand, as he is still in the first 15 hours of his regeneration cycle.
 * The Doctor assumes he has become rude and expresses dismay that he is not a ginger.
 * Harriet Jones briefly believes the new Doctor is the Ninth Doctor's son, who inherited the title.

Organisations

 * Mickey works at Clancy's.

Galactic law

 * Rose mentions the Shadow Proclamation.

Biology

 * The Doctor recognises the human blood and its blood type by taste.

Cultural references from the real world

 * The song "Rudolph the Red-Nosed Reindeer" is playing.
 * The Doctor mentions This Is Your Life.

Foods and beverages

 * The chemical components in tea can complete the healing of brain synapses and neurons recovering from the regeneration process.
 * The Doctor finds an apple in the pocket of Howard's bathrobe.
 * The Doctor uses a satsuma (also found in the pocket of Howard's bathrobe) to defeat the Sycorax Leader.
 * Jackie suggests that the Doctor needs a bowl of soup and a ham sandwich.

Medicine

 * The remedies Jackie suggests to the Doctor are aspirin, codeine, paracetamol, Pepto-Bismol, liquid paraffin, Vitamin C, Vitamin D, and Vitamin E.

Individuals

 * Luke Parsons is an A positive.
 * Mickey mentions to Rose that he and Jackie have been spending more time together, and that he goes over to her flat every Sunday for dinner where she "yaps and yaps".

Planets

 * Guinevere One was en route to Mars when intercepted by the Sycorax ship.

Species

 * Daleks, Slitheen, and the Gelth are all mentioned by Rose.
 * The weapon fired at the Sycorax was taken from a Jathaa sunglider.

Time Lords

 * While suffering from post regeneration stress, the Doctor says that he is "having a neuron implosion." Later, in reference to the cure for this malady, he mentions synapses.

Torchwood

 * This is the first time the Torchwood Institute is acknowledged to exist as a physical entity; it was first mentioned during The Weakest Link game on the Game Station. It is so secret even the United Nations does not know of its existence, and the Prime Minister isn't supposed to know, although Harriet Jones somehow does.

United Nations Intelligence Taskforce

 * UNIT has a headquarters in the Tower of London.

Technology

 * The Hubble Array is following the course of the Sycorax ship.

Ratings

 * 9.84 million

Myths

 * Some early reports suggested that the enemy would be the Cybermen. Tabloid newspaper The Sun reported that Shaun Dingwall would return as Rose's father, Pete Tyler, and that this episode would be set on an alternative Earth. However, all of these claims were proven to be incorrect when the episode was broadcast, and appear to refer to Rise of the Cybermen/The Age of Steel. Coincidentally, the Cybermen were later announced as the enemies in the later 2008 Christmas special.
 * After the announcement that Christopher Eccleston would leave after the first series, there were erroneous reports that the regeneration was to take place during the Christmas special, not during The Parting of the Ways. (This may have been an intentional red herring in order to maintain at least some element of surprise for the series finale given that the BBC had accidentally blown Russell T Davies' plan for a surprise regeneration.)

Influences

 * Besides being the name of the invading aliens, Sycorax is also the name of the witch in William Shakespeare's play, The Tempest. In the later series 3 episode, The Shakespeare Code, the Doctor accidentally gives Shakespeare the name "Sycorax" when he sees an animal skull which reminds him of one of the aliens.
 * The Sycorax, with their curse-like blood control technology and bone-motif costumes, are slightly similar to Faction Paradox, a time-travelling voodoo cult created by Lawrence Miles that were recurring villains in the BBC Eighth Doctor Adventures novels.
 * Harriet Jones's decision to destroy the Sycorax spaceship, despite the fact it was leaving Earth, echoes Margaret Thatcher's decision to sink the Argentinian ship Belgrano in the 1982 Falklands War, even though evidence suggests it was actually leaving British waters.
 * Guinevere One, the name of the probe that Earth sends to Mars, references the myths of King Arthur. In those stories, Guinevere was Arthur's Queen Consort. Her name is an old French form of the Welsh name Gwenhwyfar, which can be translated as "white shadow". Her adulterous affair with Arthur's chief knight, Lancelot, and betrayal of her husband lead to the downfall of their kingdom. When the Seventh Doctor was recognised as Merlin, Arthur's advisor, he assumed that he would later find himself in this role. (TV: Battlefield)
 * The Doctor's sword duel with the Sycorax leader, particularly when his hand is cut off, resembles the lightsaber duel between Luke Skywalker and Darth Vader in Star Wars Episode V: The Empire Strikes Back.
 * The Doctor comments that the bathrobe and pyjamas Jackie has given him to wear are "very Arthur Dent". In the short story Have You Seen This Man? on the Who is Doctor Who? website, a certain Arthur Dent mentions that the Doctor had once laid in front of a bulldozer in front of Dent's home, meaning that the reference in The Christmas Invasion is more this likely referring to this encounter between the characters. Arthur Dent is a character in The Hitchhiker's Guide to the Galaxy, created by former Doctor Who script editor Douglas Adams. Also, Jackie's line "Anything else he's got two of?" is also spoken by Arthur Dent in the 2005 movie adaptation of The Hitchhiker's Guide to the Galaxy, in reference to the two-headed Zaphod Beeblebrox.
 * When speaking to the Sycorax of the great potential humans possess, the Doctor realises he is quoting from The Lion King.

Filming locations

 * Tredegar House, Newport
 * Brandon Estate, Kennington, London (The Powell Estate)
 * Palace of Westminster, Westminster, London
 * Tower of London, London
 * Landmark Place, Churchill Way, Cardiff
 * Hayes Island, Cardiff
 * Clearwell Caves – Ancient Iron Mines, Coleford, Gloucestershire
 * Barry Docks, Barry Island, Cardiff
 * NCP Tredegar Street (also known as St Davids 2), Cardiff, Wales
 * Wallis House, Great West Road, Brentford
 * Trafalgar Square, London
 * 30 St Mary Axe (also known as "The Gherkin"), London
 * Baltic House, Mount Stuart Square, Cardiff
 * Wharton Street, Cardiff
 * Broadstairs Road, Leckwith, Cardiff
 * Brian Cox Motor Engineering, Bromley Road, Ellwood (Clancy's garage where Mickey is working when the TARDIS arrives in the teaser sequence)
 * Millennium Stadium, Cardiff
 * Unit Q2, Imperial Park, Imperial Way, Newport
 * HTV Wales Studios, Culvershouse Cross, Cardiff
 * BBC Kendal Avenue, Kendal Avenue, Acton
 * BBC Broadcasting House (C2 Studio), Llantrisant Road, Llandaff, Cardiff

Production errors

 * When Mickey calls Rose to check out the military broadcast of the Sycorax ship, you can see for a split-second the video player playing the broadcast, revealing that it was not green-screened, but a video playing on the computer.
 * Although it has been a very short time since the Doctor regenerated, as Rose passes the door of the TARDIS after the Doctor collapses, her hair is visibly longer. (TV: The Parting of the Ways) This exposes the several month break between the wrapping up of Series 1 in March 2005, and the beginning of filming for Series 2 in July, during which time Billie Piper allowed her hair to grow longer.
 * When proclaiming his new form to be "lucky", the Doctor is facing towards the Sycorax ship, but when mentioning being in the first 15 hours of his regenerative cycle, he is facing away from the Sycorax ship. He is facing the ship again when his hand regrows.
 * A lot of the shots between the Doctor winning the challenge and giving his warning to the Sycorax horde have inconsistent lighting. One notable example of this is when the Doctor throws the satsuma, the light is on the right side of his face but is then on the left side of the button the fruit hits when it should be on the right. The green screen of the ship exterior is also darkened on the left side, making this error more prominent.
 * In one of the Tower of London scenes, the Guinevere 1 Space Probe is incorrectly spelt "Guinivere 1" on a computer screen.
 * In the 2017 Series 2 Blu-ray Steelbook, Phil Collinson, the producer of this episode, is incorrectly credited after the title sequence as "Phil Collision".

Continuity

 * The Doctor's speech to PM Harriet Jones about how "Earth is drawing attention to itself" recalls a similar statement made by the Brigadier when recruiting Liz Shaw to UNIT. (TV: Spearhead from Space)
 * Jones's destruction of the Sycorax ship and the Doctor's angry reaction are similar to the Brigadier using explosives to destroy the Silurian hibernation chambers even as the Doctor departs to begin peace negotiations. (TV: Doctor Who and the Silurians)
 * The United Kingdom had previous missions to Mars. (TV: The Ambassadors of Death, PROSE: The Dying Days)
 * The Ice Warriors are actual Martians - which, as stated, look "completely different". (TV: The Ice Warriors)
 * While the Tenth Doctor, Rose and Mickey are on the Sycorax ship, Jackie has an unexpected encounter with the Third Doctor, Jo Grant and Captain Mike Yates, who unintentionally responded to Harriet Jones' distress call after it was detected by the Third Doctor's TARDIS. (PROSE: The Christmas Inversion)
 * While The Tenth Doctor and Rose were away on the Sycorax ship, the Master had broken into Jackie's flat, and she defeats him with The Third Doctor, Jo Grant, and Mike Yates. (PROSE: The Christmas Inversion)
 * The Robotic Santas reappear, under control of the Empress of the Racnoss. (TV: The Runaway Bride)
 * Harriet Jones questions if Code Nine, an Emergency Protocol which detected important words such as "Doctor" and "TARDIS", had been activated. (TV: Aliens of London/World War Three)
 * The Doctor regrows his severed hand as he retains regenerative energy for the first fifteen hours in a new body, suggesting an explanation for Romana II's ability to change her appearance several times during her regeneration. (TV: Destiny of the Daleks)
 * The Doctor's severed hand is later retrieved by Jack Harkness. (TV: Everything Changes, Utopia) Much later, it would return to the Doctor. (TV: Last of the Time Lords) It bubbled furiously when it sensed the TARDIS flying off to find Jenny. (TV: The Poison Sky, The Doctor's Daughter) After the Doctor used it as a receptacle for regeneration energy, something compelled Donna to touch the hand, enabling it to grow into the Meta-Crisis Tenth Doctor and also turning Donna into the Doctor-Donna, leading them to defeat the New Dalek Empire and stop Davros' reality bomb. The real Tenth Doctor subsequently took the Meta-Crisis Tenth Doctor to a parallel universe, leaving him to live out his life there with Rose Tyler. (TV: Journey's End)
 * While rummaging his clothes in search of what should be his new look, the Tenth Doctor passes through the Second Doctor's trousers and jacket, the Sixth Doctor's waistcoat, (TV: The Two Doctors) and a burgundy scarf. (TV: The Leisure Hive-Logopolis) In the rest of the wardrobe room, various items and articles of clothing are visible, including:
 * A brass pillar. (TV: An Unearthly Child, et al.)
 * A Third Doctor's Inverness cape hanging next to the pillar. (TV: Terror of the Autons)
 * The Sixth Doctor's coat on the other side of the pillar. (TV: The Twin Dilemma, et al.)
 * One of Steven Taylor's jumpers next to the coat. (TV: The Celestial Toymaker)
 * A grand mirror. (TV: Castrovalva)
 * Kublai Khan's cane against the mirror. (TV: Marco Polo, et al.)
 * A wooden trunk (TV: The Power of the Daleks)
 * The Seventh Doctor's umbrella in a bucket. (TV: Time and the Rani, et al.)
 * The Sixth Doctor's umbrella. (TV: The Two Doctors, Time and the Rani)
 * The Fifth Doctor's Panama hat on this umbrella. (TV: Castrovalva, et al)
 * The Second Doctor's stovepipe hat (TV: The Power of the Daleks, The Highlanders, The Underwater Menace)
 * The First Doctor's feather hat. (TV: The Reign of Terror)
 * The Fourth Doctor's brown fedora hat on the spiral stairs under the room. (TV: Robot, et al.)
 * Alydon's cloak hanging under the room. (TV: The Daleks)
 * A Fourth Doctor-like outfit, with a long coat and long yellow and red scarf, hanging from the very hatstand of this incarnation.
 * A kilt.
 * A green Edwardian coat. (TV: Doctor Who)
 * During Rose's improvised speech to the Sycorax, she resorts to name-dropping several creatures from her previous travels with the Ninth Doctor:
 * The Slitheen (TV: Aliens of London/World War Three, Boom Town)
 * The Gelth (TV: The Unquiet Dead)
 * The Mighty Jagrafess [sic] (TV: The Long Game)
 * The Daleks (TV: Dalek, Bad Wolf/The Parting of the Ways)
 * Rose attempts to invoke Article 15 of the Shadow Proclamation. (PROSE: Diamond Dogs) Presumably, she was attempting to recall Convention 15, which the Ninth Doctor had used to approach the Nestene Consciousness. (TV: Rose)
 * The ramifications of the destruction of the Sycorax vessel, including the impact on a group of female (and presumably related) Sycorax, is explored in COMIC: The Widow's Curse.
 * It also indicates that the Sycorax Leader's proclamation of "Fadros Pallujikaa" is actually his name.
 * The TARDIS is in motion as it materialises, due to the Doctor speeding it up to breakneck speeds in the time vortex. (TV: Born Again) It has materialised and dematerialised in motion before, (TV: Fury From the Deep, The War Games) and would do so again next Christmas. (TV: The Runaway Bride)
 * Jones' statement regarding the Doctor not always being available to help the planet is later echoed and discussed by Gwen Cooper. (TV: Children of Earth: Day Five)
 * The Third Doctor was revived from a trance by coffee. (TV: Planet of the Spiders)
 * The Doctor identifies the blood type through taste. Romana demonstrated a similar sensory precision in identifying a mineral's composition through taste. (TV: Destiny of the Daleks)
 * When the Doctor regenerates into the Eleventh Doctor, he complains again when he notices that he's "still not ginger"; (TV: The End of Time) the Ninth Doctor previously wondered why he'd never become ginger while examining his reflection. (PROSE: Rose)
 * Construction girders around the Clock Tower of Big Ben indicate that repair work is still being done following its recent collision with a spaceship. (TV: Aliens of London)
 * The Sycorax would later appear to be part of the Pandorica Alliance. (TV: The Pandorica Opens)
 * Harriet Jones introduces herself regularly as "Harriet Jones, Prime Minister" to which the common reply is, "Yes, I know who you are"; she did the same before becoming Prime Minister, introducing herself to everyone as "Harriet Jones, MP for Flydale North". (TV: Aliens of London/World War Three)
 * She would later continue this as former Prime Minister, with a similar response. (TV: The Stolen Earth)
 * The Doctor has previously engaged in sword fights. (TV: Marco Polo, The Sea Devils, The Masque of Mandragora, The Androids of Tara, The King's Demons)
 * The Doctor previously encountered the Sycorax and blood control in his seventh incarnation at the Blood Bank in the far future. (AUDIO: Harvest of the Sycorax)
 * By seeding the downfall of Harriet Jones as Prime Minister, the Tenth Doctor unwittingly triggered a cascade of events that would end with his demise:
 * The Doctor and future companion Martha Jones arrived at Malcassairo in the year 100,000,000,000,000 by accident. They also found that Jack Harkness hitched onto the TARDIS exterior and was dragged through the Time Vortex, trying to reunite with the Doctor after being left behind at the Game Station when he was made immortal by the Bad Wolf. (TV: The Parting of the Ways, Utopia)
 * The group met Professor Yana, who Martha noticed had a fob watch. After her experience with the chameleon arch, she thought Yana was a benevolent Time Lord that became human, but Yana's true identity belonged to the Master, who had fled the Time War. After regenerating, he stole the Doctor's TARDIS and fled the planet, but the Doctor tampered with his TARDIS to trap him on Earth. (TV: Human Nature, Utopia)
 * Jones' removal from power allowed to replace her under the identity of Harold Saxon, though he was later removed from power and shot by Lucy Saxon for tormenting her. He chose to die rather than regenerate into a new incarnation and live a life of captivity. (TV: The Sound of Drums, Last of the Time Lords)
 * The Disciples of Saxon, the Master's followers, resurrected him, but Lucy again tried to kill him and managed to damage his new body at the price of her own life. The crippled Master was soon recruited by Joshua Naismith to work on the Immortality Gate for his intellect. The Master sabotaged the Gate and used it to make the Master Race, then retrieved Gallifrey and its denizens from the Time War with the help of a White-Point Star. (TV: The End of Time)
 * During the Master's confrontation with Lord President Rassilon, Wilfred Mott rescued a trapped worker in the Gate's radiation booth and took his place. The booth's anti-leak security measures only allowed one person to exit while another person had to be locked inside. (TV: The End of Time)
 * The Doctor cut the link holding Gallifrey out of the Time War, which sent the Time Lords back into the battlefield, the Master joining them. However, he left the Immortality Gate's nuclear bolt running. It went into meltdown and the excess radiation would have dumped into the containment booth with Wilf still inside. Trying to operate the booth in any way would also have the same result. In order to rescue Wilf, the Doctor had to enter the booth and expose himself to the radiation, leading to his regeneration. (TV: The End of Time)
 * On Christmas Eve 2006, an older version of the Tenth Doctor returned to London on the day that his newly regenerated self was battling the Sycorax above the city. On that occasion, he visited a young patient at St. Nicholas's Hospital, Daniel Francis Thompson, and helped him awaken from his coma. (PROSE: Deep and Dreamless Sleep)
 * The Tenth Doctor mentions Arthur Dent. Arthur was previously seen alongside Zaphod Beeblebrox inside the Time Lord prison Shada (WC: Shada) and would write about the Doctor on the website Doctor Who?. (PROSE: Have You Seen This Man?)

Home video releases

 * A behind-the-scenes preview of this episode was released with the series 1 DVD box set.
 * As with every other episode of season 2, The Christmas Invasion was released on DVD by 2Entertain.
 * This story was released on a vanilla DVD with New Earth.
 * It was also released as part of the Series 2 DVD Box set in November 2006.
 * This story was also released with Issue 7 of the Doctor Who DVD Files.