The Doctor's Daughter (TV story)

The Doctor's Daughter was the sixth episode of series 4 of Doctor Who.

It was significant for introducing only the second known genetic relative of the Doctor seen in a televised episode in Jenny, a female created by a progenation machine from his DNA. Additionally, her fate at the conclusion of the episode left — atypically for most guest characters — obvious narrative possibilities for her return to the programme.

From a production standpoint, it was notable for its interesting casting of Georgia Moffett, the real-life daughter of Peter Davison. In giving the part of Jenny to Georgia Moffett, the production team had cast the daughter of an actor who had played the Doctor to play an on-screen daughter of the character. In addition, this episode marks the first meeting between David Tennant and Moffett; a year later they started dating, and married on 30 December 2011, nine months after Moffett gave birth to their daughter, Olive.

Synopsis
Just after finally defeating the Sontarans on modern-day Earth, the Doctor's TARDIS takes the Tenth Doctor, Donna Noble and Martha Jones on an unexpected trip to the barren planet Messaline. Arriving right in the middle of a war between humans and Hath, the Doctor meets someone he thought he never would: his daughter. Can the Doctor accept this clone as his offspring, and can he stop the war before it all ends in massacre on both sides?

Plot
The TARDIS continues to fly out of control as the Doctor's attempts to gain control of his vehicle continue failing. Martha and Donna are having trouble keeping their balance since the TARDIS's flight is more erratic than usual. The console smokes and sparks and the ship bucks violently, hurling its occupants about. The Doctor's severed hand bubbles furiously. Seeing this, the Doctor comments his old hand is "liking" their unexpected trip. Donna is horrified by this; she thought it was just a "freaky alien thing" and not the Doctor's hand. Martha explains that the Doctor's hand got cut off and he grew a new one, making Donna call the Doctor impossible. The Doctor, however, says he's not impossible, "just a bit unlikely".

The TARDIS finally lands, allowing the occupants to catch their breath. The Doctor, Donna and Martha depart from the TARDIS to find themselves in what seems to be an underground bunker. The Doctor is the most confused of the three as he has absolutely no idea why the TARDIS would bring them to a place like this. Martha says she loves stepping out of the TARDIS and into a new world, confusing Donna as she had been yelling at the Doctor to take her home. Having a laugh, Martha and Donna talk about the feeling of seeing new worlds, saying it's like having a hamster stuck in your throat.

Suddenly, armed men arrive and order them to drop their weapons; they raise their hands to show they are unarmed. However, the lead soldier, Cline, says the Doctor's hands are "clean" and has the other two soldiers take him and force his hand into a machine near by; the Doctor is confused, wondering what's wrong with clean hands. The Doctor jokes, knowing it "isn't going to take my blood pressure", as Martha and Donna ask what they are doing to him. Holding them at gunpoint, Cline explains that everyone gets processed. In between yelps of pain, the Doctor figures out the machine is taking a sample of his tissue and is using it in the "cabinet" device attached to it. The machine releases the Doctor's hand; he and a concerned Donna and Martha look down at his hand to see a y-shape cut on the back of it. The cabinet opens with a hiss of smoke and out of it comes a young blonde girl in combat attire, who is given a gun by Cline. As the girl preps her weapon, both Martha and Donna wonder who she is; a bit stunned by what he's seeing, the Doctor explains that she's his daughter. The girl smiles at him and says, "Hello, dad".

As the soldiers set up explosives on the walls of the tunnel, Cline questions the Doctor's daughter on how ready she is for combat. In the meantime, both Martha and Donna wonder how this woman can be the Doctor's daughter; he's told both of them how he became the last of the Time Lords. The Doctor explains that the machine took a sample of his diploid cells, which were split into haploids, then recombined in a new pattern and grown "very quickly, apparently" into the young girl in front of them. It makes one person biological mother and father; in short, this person just created by the machine is a kind of clone of the Doctor.

Just then, someone breaks in and Cline yells it's the Hath. Each of the armed sides fire at the other as the Doctor, Donna and Martha hide. Just as the two soldiers with Cline are shot, Martha is captured by a Hath. Cline orders the explosives to be set off. Despite the Doctor's protests, his daughter obeys and sets off the explosives, sealing the tunnel, separating them from Martha and the TARDIS.

The Doctor demands to know why his daughter did that, to which she explains is because the Hath shot at them. She calls Martha's capture collateral damage, believing him lucky; he still has Donna, but Cline lost his men. Angered, Donna tells "G.I. Jane" that Martha isn't collateral damage; they decide to go look for Martha. However, Cline points his gun at them; he's confused as they don't have marks or a will to fight. He explains that they'll be taken to General Cobb for interrogation; seeming to not understand the concept of pacifism, Cline appears to think that anyone not trying to kill the Hath is a dangerous element.

On the other side of the rubble, Martha regains consciousness to find herself undamaged and next to the TARDIS with her would-be kidnapper, who's injured. Martha instructs the Hath to be still while she examines its injury. She finds it has a dislocated shoulder but is confused if she is completely correct as a Hath is not a human. More Hath soldiers arrive and point their guns at Martha; she explains her status as a doctor and that she will not leave a patient in an injured state. She relocates the injured Hath's shoulder and the other Hath think she lied. However, the recovered Hath shows them she did help, having its comrades lower their weapons. Picking herself up, Martha greets them. "I'm Dr. Martha Jones, who the hell are you?"

Elsewhere, the Doctor and Donna are being escorted to Cline's camp and ask where they are; Cline explains they're on Messaline, or what's left of it. Donna then asks the Doctor's daughter for her name, only to find out she doesn't have one. The Doctor calls her a generated anomaly; she was bred with military knowledge and common sense, but no name. Donna decides to name her Jenny based on it, which she accepts. Donna asks the Doctor about the name, only for him to act indifferent. Donna says he's not much of a natural parent, prompting him to remind her that his DNA was stolen at gunpoint and processed. He asks her if he can extrapolate a relationship based on an accident, to which Donna points out, "Child Support Agency can". He retorts, "Just because I share certain physiological traits with simian primates, that doesn't make me a monkey's uncle, does it?" Jenny misunderstands the conversation, defending herself, "I'm not a monkey... Or a child".

They arrive in the camp to find the human group lives in a theatre; Cline orders them to stay still while he talks to Cobb. Donna is shocked by this, but the Doctor jokes, "Maybe they're doing Miss Saigon". Cline walks over with an elderly man, whom the Doctor addresses, "General Cobb, I presume?" Cobb explains the Doctor and Donna were found in the eastern tunnels and with no marks, going on to explain there were pacifists three generations back before they lost contact; he wonders if they are generations from the pacifists. The Doctor decides to pick up on this easily given lie and says that they are from the eastern zone and asks who the Hath are.

In the meantime, Martha has been brought back to the Hath camp and is given a warm welcome due to helping one of their comrades. She is a bit uncomfortable with the attention but is glad they are not trying to kill her. The Hath are likely happy to have a medic on their side.

Back in the human camp, Cobb explains long ago the buildings were built into the ground as the environment is too hazardous. Donna finds a fault with the story; there are windows, leading to confusion as to why there any constructed at all since the outside is too dangerous. Cobb explains Hath and humans decided to build a new society together, but the dream died; the Hath wanted Messaline for themselves, forcing the first colonists to use the machines to produce soldiers and began the war. The Doctor wonders what they are fighting for and Cobb explains a myth about how a Goddess created the universe, looked at her work and sighed. That sigh was caught in some form which is now referred to as "the Source". They believe the Source to be lost in the maze of tunnels they show the Doctor on a holographic map. Recovering it could allow them to exterminate the Hath and win Messaline for themselves.

Meanwhile, the Hath are showing Martha an identical holographic map. Martha appears to partially understand them thanks to the TARDIS translation circuits; she had never gone anywhere in time with the Doctor where English wasn't spoken. She points at a section of the map, believing it to be where they are; however, all she earns are sighs due to being wrong.

Back at the human camp, the Doctor wonders if the map covers the Hath part of the city as well, which Cline answers yes; he says it will help them find Martha. Cline says they have more important things to do, but when it's morning, they can use the machines to create a platoon. Donna is mortified at the idea of using a machine to have offspring, apologising to Jenny as she does not see her as a real person. Jenny defends herself by saying she has free thought and will, making her just as real as Donna and the Doctor, wondering how they differ. Cobb shows pride in Jenny, wishing he had more soldiers like her. Yelling in success, the Doctor explains there's a suppressed layer of information and uses his sonic screwdriver to reveal a previously unknown route to the Temple where the Source is located.

At the same time, the Doctor's meddling with the human's map has accidentally allowed the Hath to see the new route on their map as well. Martha explains what they are seeing in surprise, but the Hath think she has done something to help them and they pat her on the back, congratulating her for her help. Martha looks on as the Hath wave their weapons. Horrified, Martha thinks she has started a war.

Cobb orders to prepare for a final battle for "peace in their time"; however, the Doctor asks why they don't simply stop fighting. Cobb explains once the Source is in their possession, they can wipe out the Hath. The Doctor points out that's contradictory as genocide is the opposite of peace, but Cobb says its the same result in war. Seeing Cobb's insane, the Doctor tells him, "You need to get yourself a better dictionary. When you do, look up genocide. There'll be a little picture of me there and the caption will read, 'Over my dead body!'" Cobb mocks the Doctor for showing his army the way to the Source and orders Cline to take arms, threatening to kill his woman (Donna) if he interferes. Both the Doctor and Donna dismiss the idea they are together before Cobb orders Jenny imprisoned with them as she's "from pacifist stock" and can't be trusted.

Once inside the cell, Donna notices there's another plaque with numbers and wonders what they mean. The Doctor tells her they make as much sense as the story Cobb told them, prompting Donna to wonder if it's true. If "the Source" exists, it could actually be a weapon, instead of something mythical. Donna is annoyed that they "gave directions to Captain Nutjob". The Doctor decides they have to come up with a plan to escape and stop the ensuing bloodbath; Jenny looks at him in confusion. Equally confused, he asks why Jenny is staring at him. Jenny says that despite saying he is not a soldier, the Doctor is making plans like a proper general. The Doctor tells her that he is trying to stop the fighting without violence. Jenny tells him every soldier is.

Annoyed and not knowing what to say, the Doctor puts the idea aside for now and asks Donna for her mobile, saying it's time for an upgrade. The Doctor takes out his sonic screwdriver, and Jenny says he has a weapon now. Further annoyed, the Doctor tells her it's not a weapon while she laughs that she will learn so much from him as he is "such a soldier". Speechless, the Doctor tells Donna to talk to Jenny, but Donna is enjoying watching this and encourages Jenny to keep going. The Doctor calls Martha and is relieved she is alright and explains he, Donna and Jenny are as well. However, he becomes grim when he learns his meddling with the map gave the Hath the same directions to the Source as Cobb. The Doctor instructs Martha to stay where she is and to be safe as Martha's phone battery goes dead.

Meanwhile, Martha and the Hath she healed, Peck, are studying the tunnels as she wonders if there is some place where she can recharge her mobile. Peck works the controls and converts the map into 3D, delighting Martha. Noting that the distance above ground is shorter than the distance through the tunnels, she plans to beat both the humans and the Hath to the Source. However, Peck informs her that it's a bad idea as the surface has low radiation levels; Martha decides that small time exposed to it wouldn't have any lasting harmful effects.

Elsewhere, Donna forces the Doctor to accept Jenny as his offspring by using his stethoscope to show him that she has two hearts, proving she is the same species as him. The Doctor, however, insists that Time Lords are defined by their shared tragedy and therefore Jenny is not a Time Lady; Jenny is confused by this as she had only the knowledge of this planet in her head. The Doctor explains that it all vanished in the Last Great Time War, a war much bigger than this one; he admits to killing in the war, which he greatly regrets. Jenny then asks how they are different.

In the meantime, the Hath have found their side of the entrance into the Temple and use a battering ram to create a shortcut. Martha and Peck reach a hatch and escape to the desolate surface while Martha berates Peck for using foul language when she says he couldn't resist seeing the surface.

Back at the cell, Jenny seduces the guard and then holds him at gunpoint to force him to open the door. Amused, Donna tells the Doctor, "I'd like to see you do that". The Doctor only gives an embarrassed look as they escape. They reach the exit of the camp, only to find another guard. Donna offers to distract this one, but the Doctor tells her that she should save her "womanly wiles" for an emergency; Donna knows he is lying, but agrees. Using a toy mouse, the Doctor distracts the guard, but Jenny knocks him out with a karate chop. Annoyed, the Doctor tells her to "stand still, don't hurt anybody", while he searches the guard for a copy of the new map.

On the surface, Martha falls down a scree into quicksand. Peck leaps in to save her, getting her to the edge of the quicksand, where she climbs out. However, Peck is unable to get out himself; he sinks beneath the surface, content to have saved her. Martha is devastated and weeps bitterly as the wind howls and her friend disappears beneath the surface.

Elsewhere, the Doctor, Donna and Jenny have found the secret entrance. Donna finds a plaque, asking for a pen and paper from the Doctor as she notes the plaques are counting down the closer they get. Jenny notes they're always thinking, which is new to her, having been bred to follow orders and asks who the Doctor is, only to get "the Doctor" as an answer; she wonders if he's an anomaly, too. The Doctor says he's not, while Donna says "You're the most anomalous bloke I know". Jenny asks what they do; Donna says they save planets, rescue civilizations, defeat terrible creatures and do an awful lot of running - "seriously, there's an outrageous amount of running involved". Donna asks the Doctor if Jenny will join them, to which the Doctor agrees to. They get the door open just as Cobb's army arrives and seal it shut behind them.

After Jenny runs ahead to scout, the Doctor explains to Donna his previous parenting, the pain of losing the Time Lords and his family, and the fact that he is reminded of them when he sees Jenny. They come across a security grid and the Doctor shuts it off just as Cobb and his men break through the door. This gives Jenny a choice: follow her dad or shoot Cobb. She shoots a pipe to release some steam to buy time but doesn't make it back to the Doctor in time as the security beams come back on. Jenny abandons her gun and flips through the beams, astonishing the Doctor and Donna. The Doctor yells to Cobb that if the Source is a weapon, he's going to destroy it, while Cobb threatens the Doctor's life, saying one of them will die, but not himself.

The Doctor, Donna, and Jenny discover the Temple is the original spaceship. He is puzzled to find the ship so well-maintained, despite supposedly having being abandoned for years. They find a computer that says the colonisation mission commander died of Byzantine fever, causing a power vacuum between the humans and Hath. Donna stares at a digital clock on the wall and suddenly realises what the numbers are... dates; the city was built in sections outward from the ship and the dates (which aren't counting down, but counting out) mark when each section was completed. The Doctor praises Donna for her discovery, but Donna tells him that he still doesn't get it. Upon examening the date again, the Doctor realises what Donna is talking about; according to the dates, the ship landed only seven days ago. The "generations" mentioned by the soldiers aren't years; they refer to the generations bred from the Progenation machines.

They proceed up the stairs, finding Martha, who tells them she took the surface route. At the same time, the Hath and Cobb's forces are cutting through the doors to get inside the ship. The quartet suddenly smell flowers and race to the very top to find a garden kept alive by the Source, a terraforming device to make hostile environments habitable. The original colonists likely died a few days into the war, leaving the soldiers with inaccurate information, leaving them to speculate; this caused them to fight over nothing.

The human and Hath armies arrive, confused, wondering if it's a trap. The Doctor explains that they no longer really know why they're here as their history is getting more distorted the more it's passed on, like Chinese whispers. The Doctor, surrounded by both armies, declares the war over and smashes the Source to release its gases and start the terraforming process. Both armies lay down their weapons in awe of the new planet forming around them. Jenny wonders what is happening and the Doctor tells her the gases will escape to the outside, triggering the terraforming process, and a new world will be born.

However, Cobb, full of malice out of being denied his murder of the Hath, takes a shot at the Doctor. Jenny takes the bullet instead. Both the human army and the Hath army look on in sadness as Cline and two soldiers hold Cobb down. Donna asks Martha if Jenny is going to be okay. However, when Martha takes Jenny's pulse, she gives a grim look, signifying she won't make it. Jenny dies in the Doctor's arms, happy that he invited her to travel with him. The Doctor cries, saying that if they just wait, maybe Jenny will regenerate. However, Martha gently says that she must not be enough like the Doctor to regenerate. The Doctor replies that she was too much like himself.

After he lays her head gently on the ground, the Doctor grabs Cobb's gun and holds it to the general's head, shocking Martha and Donna as he despises guns and violence. Cobb is equally shocked, moreso when the gun is lowered. The Doctor looks him straight in the eyes and says in a soft, cold tone, “I never would”. Yelling in grief, the Doctor asks that both armies let the idea of a man "who never would" be the foundation of the Hath-human society that must now emerge. The Hath and humans ask the Doctor to allow them to give Jenny a proper funeral, to which he sadly agrees.

Later, the Doctor concludes that Jenny's creation was the reason the TARDIS had brought them to Messaline. The only problem was that they had just gotten there a little too soon; thus they ended up creating Jenny in the first place - "Paradox, an endless paradox" the Doctor quips. He returns Martha home, where Martha and Donna talk about travelling with the Doctor. Donna tells Martha, "I'm going to travel with that man forever", before returning to the TARDIS. Martha hugs the Doctor and bids him goodbye, and the Doctor bids goodbye to Dr Jones, returning to the TARDIS.

Back on Messaline, Hath Gable and Cline look at Jenny's body in sadness. Suddenly, she breathes out a glowing cloud of green and gold and revives, just as the Doctor had hoped. She smiles and says, "Hello boys", before running off into the ship. Gable and Cline follow her to find she is taking one of the escape shuttles to leave the planet. A concerned Cline asks her what she is doing over the intercom and Jenny asks if he is going to tell her dad on her, saying she has a lot to see, planets to save, civilisations to rescue, monsters to defeat, and an awful lot of running to do.

Cast

 * The Doctor - David Tennant
 * Donna Noble - Catherine Tate
 * Martha Jones - Freema Agyeman
 * Jenny - Georgia Moffett
 * Cobb - Nigel Terry
 * Cline - Joe Dempsie
 * Hath Peck - Paul Kasey
 * Hath Gable - Ruari Mears
 * Carter - Akin Gazi
 * Soldier - Olalekan Lawal Jr

Uncredited cast

 * Cash - Ben Ashley
 * Hath - Jon Davey, Joe White, Sean Saye, Richard Tunesi, Pete Symonds, Oliver Hopkins, Ken Hosking
 * New Hath - Adam Sweet

Worldbuilding

 * Messaline has high radiation and an Earth-like atmosphere.
 * Donna tells the Doctor that her friend Nerys "fathered twins using a turkey baster".
 * Donna calls the plants created by the terraforming device Kew Gardens.
 * Donna calls Jenny "G.I. Jane" and nicknames Cline "Rambo".
 * The Doctor smells Bougainvillaea.
 * Cash is one of the soldiers that is killed.

Influences

 * Jenny's impressive acrobatics in a corridor full of deadly laser beams was inspired by Britney Spears' "Toxic" video. Funnily enough, the song was played in The End of the World.

Story notes

 * Russell T Davies has stated that this episode "does exactly what it says on the tin". Stephen Greenhorn's episode has the Doctor facing a dilemma unlike any before, and it is wildly different to The Lazarus Experiment. He also said that his episode was designed by Russell to "change the Doctor" in a big episode that will have "a real impact on him" and that, in terms of the series continuity, it will be a "lasting impact". This was inspired by Greenhorn stating in a Doctor Who Magazine interview that the Doctor doesn't change.
 * Stephen Greenhorn wrote The Lazarus Experiment, which coincidentally was also the sixth episode of the series it was in and also followed a two-part story by Helen Raynor that featured a returning enemy.
 * The Source is similar to many science fiction atmospheric regeneration devices. Especially like the (G.E.C.K.) in the Fallout series, in that it was also made in a lab and intended to revive a barren wasteland (post-apocalyptic earth in the Fallout series).
 * The two Hath named in credits would appear to be named after famous actors, "Hath Peck" drawing his name from and "Hath Gable" taking his from actor Clark Gable. Whether this is deliberate or a mere coincidence is uncertain.
 * According to the BBC Podcast, Russell T Davies said the original intention was to kill Jenny off at the end of the episode. It was Steven Moffat who expressed the desire to bring her back to life. According to Moffat and the BBC official book Companions and Allies, Jenny did not regenerate but was brought back to life by the Source.
 * The humans' weapons are modified real-life weapons. For example, Jenny enters the episode and is given a modified P90 with a long silencer and a longer butt stock.
 * At the end of this episode, Jenny escapes from Messaline in a stolen spacecraft to travel the universe. This mirrors her father's actions. Stylistically, the interior walls of the craft Jenny steals is reminiscent of the TARDIS' interior throughout the original series.
 * When Jenny escaped from Messaline, this led to speculation that she might reappear in later episodes.
 * This is one of the rare times in the series where an alien language is not automatically translated for the audience. (TV: The Christmas Invasion) In this instance, however, it is only the audience who cannot understand the alien language, as Martha appears to have no trouble understanding the Hath. The Hath dialogue was written in the script in English so the actors understood it.
 * The Doctor threatening to shoot Cobb was a late change. Originally, he was taken away to be executed.
 * After filming Time Crash, Peter Davison told Georgia Moffett "[now] it's your turn". They'd previously worked together in Red Dawn.
 * A protest regarding school closures took place outside Cardiff City Hall, prompting Hath Camp scenes to be postponed for a few days.
 * The Hath initially fought humanoids called the Takrans, but the pronunciation of the name was found to be ambiguous, and Russell T Davies eventually decided that it was simpler if the Hath's opponents were simply humans.
 * Even though they communicated by gurgling, Stephen Greenhorn wrote all of the dialogue for the Hath to give the actors under the masks an impression of how their characters should behave.
 * The script evolved considerably during its development, with various plot points - such as the war's seven-day length, Donna's investigation of the mysterious numbers, and the greenhouse venue of the climactic scenes - added to later drafts.
 * The underground war and the Hath's mode of communication via bubbling liquid were Russell T Davies' ideas.
 * The one line said by the soldier was deleted in post.
 * This episode formed Block Six of season four, along with Midnight. Alice Troughton would initially focus on Midnight, since it was being double-banked with Block Seven, which consisted solely of Turn Left.
 * Georgia Moffett had previously auditioned for Rose Tyler, but was deemed too young-looking. She originally auditioned for the role of Ada Mullins in The Unicorn and the Wasp.
 * Georgia Moffett hadn't been interested in the series, until her young son, Ty, became an avid devotee.
 * During production, it was announced that Julie Gardner was stepping down as both the executive producer of Doctor Who and the Head of Drama for BBC Wales.
 * David Tennant had recently concluded a two-year romance with Sophia Myles and had formed a good relationship with Georgia Moffett's son, Ty, during his visits to the set. The pair began dating soon after production wrapped and would marry on December 30th, 2011, with Tennant becoming Ty's adoptive father.

Ratings

 * Final BARB ratings - 7.33 million viewers
 * Sunday night BBC3 repeat - 0.95 million viewers

Studio

 * Upper Boat Studios, Trefforest

Location

 * Aberbaiden Open Cast Colliery, Nr Kenfig
 * City Hall, Cardiff
 * Newbridge Memorial Hall, Newbridge
 * Dupont Building, Pontypool
 * Plantaisia, Swansea
 * Rhondda Heritage Park, Nr Pontypridd
 * Johnsey Estates, Pontypool
 * Barry Shooting Range, Barry Island
 * Mark Street, Cardiff
 * Roath Conservatory, Cardiff

Myths

 * Jenny would be Susan's mother. This proved to be false.
 * Other rumours reported online included the possibility of Jenny being Rose Tyler's offspring (owing to both being blonde and also because of Rose's background appearances thus far in the season), which was disproven in the pre-credits teaser.
 * It was also rumoured that Jenny was a clone, a hologram, an illusion or something of that sort. All of these proved to be false, to one degree or another. Technically Jenny is not a clone; she is actually the Doctor's daughter, via asexual reproduction through a process similar to parthenogenesis.
 * The initial televised trailer showed Jenny kissing an individual on the mouth; due to the fast-cut editing of the trailer, the gender of the individual being kissed was not clear, leading to speculation, ultimately debunked by the episode itself, that Jenny would engage in a same-sex kiss — the character being kissed turned out to be male.
 * As Steven Moffat is credited with "saving the life" of the character by suggesting to Russell T Davies that she not be killed off, a claim Moffat has downplayed if not disputed, rumours emerged that the character may return either as a guest, a recurring role, or as a companion in 2010 when Moffat took over. Although Georgia Moffett is on record as being willing to return to the role, the character did not reappear at that time.
 * A rumour related to the above had Jenny returning for the Series 4 finale; except for a brief flashback appearance recalling her "death", she did not.

Production errors

 * At one point in the TARDIS, a studio light is visible near the right of the controls.
 * As the Hath carry the battering ram, the leader holds up a hand to stop the others. However, the Hath can be clearly heard to say "Halt!", despite the species communicating only via bubbles and groaning.
 * When Martha enters the spaceship after travelling the surface it cuts to the Doctor, Donna, and Jenny but when they cut back to Martha it shows her entering again but from a different angle.
 * During the scene where Donna, the Doctor and Jenny try to get past the laser beams, the laser beams change positions between shots.

Continuity

 * Martha is kidnapped. (TV: Gridlock, The Sontaran Stratagem)
 * The Doctor mentions his family. (TV: The Tomb of the Cybermen, Delta and the Bannermen) He had previously mentioned to Rose, "I was a dad once." (TV: Fear Her)
 * When Dr. Constantine commented, "Before the war, I was both a father and a grandfather." The Ninth Doctor replied, "I know the feeling." (TV: The Empty Child)
 * Susan Foreman was the Doctor's granddaughter (TV: An Unearthly Child onward)
 * The Doctor previously refused to kill people out of vengeance if he could help it, in this case, Cobb, because it was against his new philosophy. (TV: The Parting of the Ways, The Christmas Invasion) He would later do similar in his eleventh incarnation. (TV: A Good Man Goes to War)
 * Martha mentions the events of the sword fight with the Sycorax (TV: The Christmas Invasion) when discussing the Doctor's hand, which she learned of later. (TV: Utopia) Donna indicates that she wasn't aware of the origins of the hand before this point.
 * The Doctor cradles Jenny when she apparently dies, much as he did with . (TV: Last of the Time Lords)
 * The wound on the Doctor's hand after being processed is the same shape as the one on the hand of the Empty Child. (TV: The Empty Child/The Doctor Dances)
 * Jenny would be among those remembered when Davros asked the Doctor: "How many have died in your name? (TV: Journey's End)

Home video releases

 * This story was released in the Series 4 DVD box set in November 2008 along with the rest of the series.
 * It was released as Series 4 Volume 2 in a vanilla edition with The Sontaran Stratagem, The Poison Sky and The Unicorn and the Wasp.