Doctor: Matt Smith (Eleventh Doctor)
Companions
Karen Gillan (Amy Pond)
Arthur Darvill (Rory Williams)
Others
Mark Williams – Brian Williams
Steven Berkoff – Shakri
Stephen Blything – Henry
Jemma Redgrave – Kate Stewart
Selva Rasalingham – Ranjit
Alice O'Connell – Laura
Alan Sugar – Himself (uncredited)
Brian Cox – Himself (uncredited)
Production
Directed by Douglas Mackinnon
Written by Chris Chibnall
Produced by Marcus Wilson
Executive producer(s)
Steven Moffat
Caroline Skinner
Incidental music composer Murray Gold
Series Series 7
Length 45 minutes
Originally broadcast 22 September 2012
Amy and Rory adjust to normal life without traveling with the Doctor.
One day, billions of small black cubes appear across the globe. The Doctor arrives and he, Amy, and Rory are taken to UNIT headquarters, where Commander Kate Stewart explains that they have not been able to analyze the cubes' function. The Doctor waits with Amy and Rory for several days to monitor the situation, and gets to know Rory's father, Brian. The Doctor deems the cubes harmless and departs, though instructs Brian to keep watch.
A year passes, with Amy and Rory periodically travelling with the Doctor. Brian, after observing Amy and Rory returning from one trip, asks the Doctor what has happened to his past companions. The Doctor tells some had met a sad fate but he will not let that happen to Amy or Rory. Humanity forgets about the cubes, using them as paperweights or other functions.
A year after their arrival, the cubes start to activate, scanning information networks and act in self-defense. The Doctor fears this was a "slow invasion", and goes with Amy to UNIT while Rory and Brian help at the hospital. All the cubes are now showing the same countdown timer. When they reach zero, the cubes open, but appear empty; however, massive numbers of cardiac arrest cases are reported, killing about a third of humanity, and the Doctor finds one of his own hearts has stopped. As Amy helps him to restart his heart, Kate finds the boxes emitted a signal traced to seven sites across the globe, including the hospital Rory works at.
At the hospital, Brian has been taken by two orderlies under the control of a young girl with a cube. Rory follows them to the lift and discovers the back of it masks a portal to a ship in Earth's orbit. The Doctor and Amy arrive, discover the girl, find she is an android, and disable her. They discover the portal, and join Rory as he frees Brian. The Doctor is confronted by a hologram of a Shakri, who, according to Gallifreyan legend, were self-appointed "pest controllers" in the universe. The Shakri released the cubes to Earth to wipe out humanity and prepare to send out more, but the Doctor reverses the cubes' function, sending a signal that brings those harmed back to life. Feedback from this causes the ship to explode, though the four escape safely.
As Earth recovers, the Doctor prepares to leave alone, but Brian insists he take Amy and Rory on a once-in-a-lifetime adventure, asking "just bring them back safe".
The Power of Three