The Power of Three (TV story)

 was the fourth episode of the seventh series of Doctor Who produced by BBC Wales. It contained the reappearances of Brian Williams and UNIT. Kate Stewart, daughter of the Brigadier, made her first appearance in a piece of BBC-produced television.

The final scene of the episode, in which the Eleventh Doctor, Amy and Rory enter the TARDIS was the last regular scene filmed with Karen Gillan and Arthur Darvill in their roles.

Synopsis
There have been many ways to invade the Earth, and the Eleventh Doctor has seen them all – or so he always thought. And then the human race wakes up one morning and discovers the world has been overrun by small cubes, which then proceed to do nothing at all. A plan is afoot, humanity is endangered – but by what and how and, above all, when? Thus begins the Year of the Slow Invasion.

For the first time in his world-saving career the Doctor has to call upon one of the least of his virtues: patience. And the Ponds face something possibly more terrifying than any world-ending apocalypse: the Doctor is moving in!

Plot
In July, Amy and Rory return home after a trip with the Eleventh Doctor. They have been gone long enough that much of the food in their refrigerator has spoiled, their dirty laundry is pungent, and 59 messages have accumulated in their answering machine. After realising that they lead two lives, their life with the Doctor and their everyday life, Amy and Rory conclude that they should choose one to stick with; but then are whisked away on another adventure with the Doctor. After returning home, the couple settle back into routine. Life with the Doctor is mad and wonderful because there's always something interesting around the corner; every day life on Earth is, well, rather dull, predictable and uninteresting. Every time that Amy and Rory go away with the Doctor, they become a part of his life; however, he has never stuck around long enough to become a part of theirs; until now.

As Amy and Rory sleep, a mysterious black cube materialises in their room. They're awoken the next morning by Rory's father, Brian, who gets them to notice that many black cubes are filling the streets. They go outside and find the Doctor examining a cube in the park right across the street. Several news reports show that the cubes are all over the world, and every specialist in the unusual and alien are trying to figure out what the cubes are. Some speculate that this could be the most clever marketing campaign ever.

In the meantime, the Doctor and his family examine the cubes in the TARDIS, which he has moved into Amy and Rory's flat. Brian makes several possible guesses as to what the cubes could be, such as spaceships and pieces of a puzzle; the Doctor congratulates him on his theories. Instructing Brian to watch the cubes for any activity, the Doctor takes some equipment from the TARDIS, planning to turn the Ponds' kitchen into a makeshift lab. Rory goes to dress for work, surprising the Doctor. Amy asks what he thinks they're doing when not travelling with him; the Doctor retorts, "mostly kissing, I guess". Setting up his equipment, the Doctor learns Amy now writes for a travel magazine, having given up her modelling job, and that Rory works part-time at a hospital.

As they continue talking, a UNIT strike team breaks into the flat, bringing a trouser-less Rory into the kitchen with them. A woman named Kate Stewart walks in and apologises for the rudeness of the UNIT soldiers. She uses a device to X-ray the Doctor and confirm his identity; from UNIT's reports, the Doctor has two hearts and has a strange dress sense. Kate goes on to explain that a spike in artron energy tipped them off to his presence. They need the Doctor's expertise to deal with alien threats they haven't dealt with. She continues, saying that they've tried destroying the cubes by several means; the cubes survived plus and minus 200 Celsius, simulated five miles of water depth, being dropped out of a helicopter at 10,000 feet, and being rolled over by their best tank. The Doctor decides that the best thing to do is observe the cubes.

After UNIT departs, the Doctor watches the cubes with Amy and Rory, but quickly becomes bored. Needing to be constantly busy or risk the loss of his sanity, the Doctor performs several different tasks; he paints the Ponds' fence, practices with a football, and vacuums their flat. Seeing that it only took him an hour to do these things, the Doctor prepares to go off and have a few adventures to restore his sanity. Finding Brian hasn't moved since he ordered him to watch the cubes, the Doctor instructs him along with Amy and Rory to continue monitoring them; if they need him, they know his phone number.

As time goes on, Amy and Rory live their normal lives, taking on commitments. In October, Amy promises to be a bridesmaid at her friend Laura's future wedding, while Rory agrees to work full time at the hospital. Both tell each other what they did, finding it a bit odd as they're so used to travelling with the Doctor. In the meantime, Brian has been keeping a log; he watches the cube when he's awake and records it when he's asleep. Rory mocks him for near-religiously following the Doctor's orders, but Brian remains adamant and continues his log. At this time, the cubes have become part of every day life, being used for multiple different tasks.

During December, Rory deals with a repeat patient while a small girl appears to be possessed by her cube. An old man is in his room, waiting to be given his medication and discharged as an orderly enters, asking if he needs anything. He says no as a second enters; the old man asks this orderly to have the other leave. Despite his protests that he doesn't need help, the orderlies try subduing him. In the middle of his struggle, he removes one of their masks, revealing their inhuman nature. As the old man screams, the little girl (who had also entered the room) looks on with an expressionless face.

During the Ponds' anniversary, 26 June Amy phones the Doctor, wondering where he is. He arrives with a bouquet just as she finishes her call. He takes Amy and Rory with him to the Savoy Hotel's opening night in 1890 as his anniversary gift to them. However, despite his promise that nothing would go wrong, they ended up having to stop Zygons, who had replaced half the staff, from trying to remove their spaceship from underneath the hotel. They continued to go on several trips, during which Amy accidentally married Henry VIII.

Eventually, the Doctor takes them back home to finish their anniversary with friends and family. Brian, noticing that Amy and Rory are wearing different clothes from before they left with the Doctor, asks him how long they've been gone. Explaining that it's been seven weeks, the Doctor is asked what happened to all his previous companions. With a look of regret, the Doctor explains that some of them have left willingly or he purposely left them behind, and very few have died. However, he promises Brian that he will do everything he can to makes sure Amy and Rory don't die while travelling with him. Admitting to Amy that he misses them, the Doctor asks if he can stay with her and Rory.

During July, exactly one year after the cubes appeared, Brian prepares to take a nap while his camera records for him; the cube spins slightly after he closes his eyes. Noticing this, he tricks it into thinking he's asleep, catching it spinning. At the Ponds' flat, Rory sees a cube open on the side opposite of him. He tries to see what's inside of it, only to have the device toy with him and open on sides he can't see. Amy sees one glow and touches it, only for it to prick her with needles and take her pulse. Playing a tennis game on the Ponds' Wii, the Doctor sees a cube float in front of the screen. He threatens that if the ones who created it wish to harm humanity, he will defend them to his last breath; it fires a laser, forcing him to flee into the hall.

Brian arrives just as everyone meets and talks over each about what their cubes are doing. The Doctor looks back to see that his cube surfed the web and that there are news reports saying that some of the cubes have caused injuries all around the world. Rory is called in to assist with those injured in the area; Brian goes with to offer any assistance he can. The Doctor discovers a message on his psychic paper, telling him to go to the Tower of London, which houses one of UNIT's bases. Kate explains that several of the cubes captured by them each display only one unique function; some harmful ones are spewing fire or causing mood swings, while the harmless ones do things such as playing the "Chicken Dance" in an endless loop. He sets a computer to look for the source of the signal activating the cubes.

Noticing that Kate is beginning to panic, the Doctor tells her not to despair as her dad didn't. Kate is left shocked as how the Doctor figured out her identity; she's the daughter of his old friend, the Brigadier. He questions her as to why she dropped "Lethbridge" from her name, learning she did so to not get any favours from those in UNIT who knew the Brig. Kate explains that her dad taught her everything he could and that, in the words of his old friend, "Science will lead," explaining why she took the position of Head of Scientific Research. The Doctor smiles. Suddenly, the cubes become inactive after 47 minutes. The Doctor is left confused and goes outside, complaining about the lack of ventilation underground bases have.

At the hospital, Brian crosses paths with the identical "orderlies" while trying to find supplies Rory needs to treat patients. Having been discovered, Brian is kidnapped as well.

Outside the Tower, the Doctor and Amy debate the merit of travelling the way they do; Amy considers it "running away" and the Doctor considers it "running to". During their conversation, the Doctor realises the cubes acted out to gain attention and scan the entire planet. The power at UNIT goes out, and the cubes start a countdown from seven. At zero, the cubes open but contain nothing. Moments pass when around the world, people start going into cardiac arrest with the Doctor experiencing heart failure with one heart. The program he set earlier to find the source of the cubes comes up on the screen, revealing seven different sources; the nearest being the hospital where Rory works. He and Amy leave for the hospital.

At the hospital, Rory is searching for Brian. Seeing him being wheeled into an out-of-order lift by the false orderlies, Rory follows only to find it empty. Touching the wall in the lift, Rory finds it now houses a portal; it takes him to an alien ship, which houses patients that have been kidnapped over the entire year. He is discovered by the two orderlies, who close in on him with sedatives.

The Doctor and Amy arrive at the hospital, looking for both Rory and Brian along with the source of the cubes' signal. He discovers the little girl with the active cube and reveals her to be a simple android overseeing the entire operation. The Doctor shuts her down, but collapses in pain as one heart is not enough to keep him alive. Amy quickly grabs a defibrillator and restarts the Doctor's other heart. Though thankful, the Doctor orders Amy to "never do that again." They discover the same out-of-order lift and use the portal it to reach the alien ship. The Doctor explains that they went through a wormhole and are outside of the universe now.

They find Rory unconscious and quickly wake him. The Doctor disables the orderlies while ordering Amy and Rory to return everyone that was kidnapped through the portal. A humanoid appears in front of them, looking at the progress the cubes have made on a monitor. The Doctor explains that this being is one of the Shakri, who in the Doctor's opinion are the "pest controllers of the universe". They consider humanity to be a plague that must not be spread, hence why they've chosen to start killing them; the stolen electricity was used to exterminate a third of the human race. The Doctor says that humanity has done more good than harm, willing to defend them against the Shakri regardless of what they believe.

The humanoid vanishes, confusing Amy. The Doctor explains it was simply a hologram produced by the ship; similar to an "interactive propaganda poster". Fiddling with the controls, the Doctor reverses the process and restarts the hearts of everyone killed by the cubes. However, as a downside, the ship will explode; the Doctor, Amy and Rory are forced to flee, barely making it back.

After having dinner with Amy, Rory and Brian, the Doctor prepares to take off for solo adventures again. However, Brian encourages Amy and Rory to return to being full-time companions as travelling with the Doctor gives them the chance to save the world and make it better. The Doctor agrees, even offering Brian a place in the TARDIS. However, he turns it down, saying that someone has to stay behind and water the plants. The Doctor and the Ponds board the TARDIS and shut the door.

Amy narrates, saying "So that was the year of the slow invasion, when the Earth got cubed, and the Doctor came to stay. It was also when we realised something the Shakri never understood. What cubed actually means. The power of three."

Cast

 * The Doctor - Matt Smith
 * Amy Pond - Karen Gillan
 * Rory Williams - Arthur Darvill
 * Brian Williams - Mark Williams
 * Kate Stewart - Jemma Redgrave
 * Shakri - Steven Berkoff
 * Ranjit - Selva Rasalingam
 * Laura - Alice O'Connell
 * Arnold Underwood - Peter Cartwright
 * Orderly 1 - David Beck
 * Orderly 2 - Daniel Beck
 * UNIT Researcher - David Hartley

Uncredited cast

 * Brian Cox - Himself
 * Lord Sugar - Himself

Communications technology

 * Kate mentions iPads, Flickr, YouTube and Twitter. The mention of Twitter particularly evokes great annoyance in the Eleventh Doctor.

Culture

 * When listing things "important" about the number seven, the Doctor says, "Seven Streams of the River Ota". This is a play by.
 * When Amy calls the Gallifreyan bedtime story about the Shakri weird, the Doctor remarks, "You can talk. Wolf in your grandmother's night dress?" in reference to the story Little Red Riding Hood.
 * The Doctor tells Amy, "Through the looking glass, Amelia," in reference to Through the Looking Glass by Lewis Carroll.

The Doctor

 * The Doctor states that he keeps returning to Amy because she was the first face his eleventh incarnation laid eyes on.

Energy and radiation

 * Kate traced artron energy levels to find the Doctor and then identifies him due to his fashion sense and binary vascular system.

Foods and beverages

 * The Doctor states that he invented the Yorkshire pudding.
 * The Doctor, Amy and Rory eat fish custard.

Game consoles

 * The Doctor plays tennis on the Nintendo Wii.

Individuals

 * When Brian asks the Doctor what happened to those who previously travelled with him, he tells him that some left him, some got left behind, and some died.
 * Amy accidentally marries Henry VIII, making her the step-mother of Elizabeth I and thus the Doctor's mother-in-law twice over. (TV: The End of Time)
 * While playing virtual tennis, the Doctor mentions the tennis player Fred Perry and a pair of shorts he had borrowed from him.
 * The real physicist Brian Cox plays himself as he is interviewed on the news for an opinion about the cubes.
 * Amy estimates that she and Rory have known the Doctor for ten years in their personal timestream.

Music

 * The song "Merry Xmas Everybody" by the rock band Slade is briefly heard in the hospital.
 * One of the cubes plays the "Chicken Dance" song (aka "The Birdie Song") on an endless loop. The Doctor seems annoyed.
 * The song "Titanium" plays at the party Amy attends.

Species

 * There were Zygon duplicates at the Savoy when Amy, the Doctor and Rory visit, and the Doctor claims there is a Zygon spaceship beneath the hotel.

Substances

 * The Doctor revives Rory with Saborian smelling salts.

Story notes

 * For this episode, the Doctor Who logo's texture resembled the Shakri cubes featured prominently in the episode. Also, the shade of red in the time vortex appears to be more crimson, rather than orange, with the lightning strikes causing an additional effect of electrical surges spreading out from the tips of the bolts. The vortex also turns purple with the sharpness seriously decreasing when the Title appears.
 * The working title for this episode was Cubed.
 * The character of Kate was introduced in the 1995 made-for-video independent production Downtime.
 * As is routine for post-2005 Doctor Who, a "NEXT TIME" trailer for the next episode is shown at the end of the episode.

Ratings
"The Power of Three" was first broadcast in the United Kingdom on BBC One and BBC One HD on 22 September 2012. Overnight ratings showed that it was watched by an audience of 5.49 million live. The final consolidated rating rose to 7.67 million viewers, making it the thirteenth most-watched programme of the week on British television, and the fifth highest rated on BBC One. The episode also received 1.3 million requests on BBC iPlayer, placing it fourth for the month on the site behind the first three episodes of the series. It also received an Appreciation Index of 87, considered "excellent".

Filming locations
Belle Vue Park, Albert Road, Penarth (filming took place on June 28 2012)

The satellite view depicting Rory's hospital and its environs was over the BBC's sprawling complex at White City, Hammersmith. The view is rotated 90 degrees, such that west is at the top of the screen. The building highlighted as the hospital is BBC Centre House.

Production errors

 * After Kate Lethbridge-Stewart enters Amy and Rory's house, we see her take out her scanner. When she originally takes it out, her screen is facing the Doctor, and in the next shot, it is facing away from him.
 * In some shots when the cubes are counting down from 7, some cubes are missing the numbers in one shot and then have them in the next.This can be seen at 28:01 when the doctor is in the room with the cube, and when the nurse is removing the cubes from the hospital at around 25:44.
 * Day 67 of Brian's log was subsequent to Laura's engagement party, the on-screen caption for which showed it to have been in October. On 26 June, Amy told the Doctor that approximately nine months have elapsed since the cubes' arrival. The on-screen caption showed day 361 of Brian's log to be in July.
 * When Amy lifts her legs to allow the Doctor to vacuum the floor beneath her feet, Karen Gillan's audio recorder can be seen in the back pocket of her jeans.

Continuity

 * Rory's father Brian reappears. (TV: Dinosaurs on a Spaceship)
 * Brian's theory that the cubes may be capsules containing minirobots is unwittingly reminiscent of a plan later implemented by Lady Cassandra on Platform One. (TV: The End of the World)
 * The Eleventh Doctor, Amy and Rory have fish custard. (TV: The Eleventh Hour)
 * Kate Stewart is the daughter of Brigadier Alistair Gordon Lethbridge-Stewart. (HOMEVID: Downtime, Dæmos Rising, The Scales of Injustice)
 * The Doctor, talking to a flying cube, says, "Is that all you can do? Hover? I had a metal dog that could do that", referring to K9. (TV: The Wedding of Sarah Jane Smith)
 * The Doctor once again asks how humans cope with just one heart. (TV: The Shakespeare Code)
 * Twitter is mentioned again; the Doctor seems similarly unimpressed. (TV: The Girl Who Waited)
 * The UNIT base beneath the Tower of London is visited. It was previously seen in The Christmas Invasion and mentioned The Sontaran Stratagem.
 * The Ponds' anniversary takes place.
 * A voice interface was last seen in Let's Kill Hitler.
 * Rory kisses the Doctor on the cheek. The Doctor previously kissed Rory on the mouth in a moment of excitement. (TV: Dinosaurs on a Spaceship)
 * The dress and hairstyle of Amy during her visit to the Savoy Hotel is similar to Tegan Jovanka's dress and hairstyle which she wore to the party aboard the Buccaneer. (TV: Enlightenment)
 * The Doctor unintentionally reveals his hiding place to Henry VIII by sneezing. In a previous adventure, whilst hiding from another king, Charles II, he gives away his location by sneezing. (TV: The Impossible Astronaut)
 * Whilst hiding from Henry VIII, the Doctor is holding a mobile phone charger, which is apparently dropped as he sneezes. (TV: A Town Called Mercy)
 * The Doctor mentions that he's run restaurants before. (PROSE: The Crystal Bucephalus)
 * The Doctor tells Brian that companions have left him, (TV: Resurrection of the Daleks, et al.) been left behind, (TV: The Dalek Invasion of Earth, et al.) and a very few have died. (TV: The Daleks' Master Plan, et al.)
 * A defibrillator has been used on the Doctor before. In an earlier instance, the defibrillation contributed to his death and/or inhibited his regeneration. (TV: Doctor Who)
 * Although he hates it, the Doctor gave a salute to Kate, like the Tenth Doctor when he was reunited with the Brigadier. (COMIC: The Warkeeper's Crown)
 * The loss of power at UNIT continues the theme of lights going out over the course of Series 7, which may indicate what will happen in the next episode, TV: The Angels Take Manhattan. Additionally, this episode features the explosion of the Shakri spacecraft, another theme of the series. Moreover, the subject of the Doctor fearing that the Ponds will fade out of his life and Brian's wishes to get them back home safely darkly foreshadows the following adventure.
 * The Doctor rambles on at the end of the episode as he thinks of things to do on his travels. He flippantly mentions "swings to... swing on." By coincidence, he ends up sulking on a swing set later on in WC: The Bells of Saint John: A Prequel.
 * The segment of the story taking place in June specifically takes place on 26 June, as Amy says in her voicemail to the Doctor that it's her and Rory's wedding anniversary. (TV: The Big Bang)

Home video releases
This episode, along with the rest of the first half of the series (episodes one through to five) was released on DVD and Blu Ray on the 28 October 2012. The short documentary A Writer's Tale focused on the making of this story.