Craig and Sophie

After the events of "The Lodger", Craig Owens and Sophie have had a baby, Alfie, and have moved into a new home. Sophie is going away for the weekend to rest leaving Craig to look after their baby son. However, soon after Sophie leaves the house, after making sure that Craig can cope with their son, Craig hears a knock on the door.

He finds The Doctor standing on his doorstep for what he claims is a social visit, but The Doctor becomes intrigued by a series of electrical disturbances. Craig suspects that there is something wrong, but The Doctor refuses to allow Craig to help. After inviting himself in The Doctor, on interpreting Alfie's cries, finds that Craig is having difficulties being a father.

The next day Craig encounters The Doctor working in the toy section of a department store, searching for the cause of the power fluctuations and the case of a missing saleswoman. Other people have been vanishing, and The Doctor is sure there is a connection to the flickering power. When The Doctor tries to get Craig and Alfie out of the shop, via a lift, they find themselves aboard a spaceship where The Doctor recognises a Cyberman heading towards them. The Doctor though manages to reverse the teleportation before they are discovered - disabling the teleporter in the process. He tries to get Craig to leave the store so he can investigate, but Craig refuses to leave as he believes the safest place for him and his son is by The Doctor's side.

The Doctor

A little later, as The Doctor gossips with Val his co-worker, he learns of a ‘silver rat’ that has been sighted in the store. The Doctor then silently observes Amy and Rory shopping, and notices that Amy is featured in an advertising poster for perfume. That night The Doctor and Craig hide in the department store and capture a Cybermat. The Doctor explains to Craig that it has been causing the power fluctuations by siphoning power to the Cybermen’s spaceship, but The Doctor is surprised by how little power it is drawing.

On further investigation The Doctor finds himself in the basement where he discovers the dead body of one of the security guards. He is then attacked by a Cyberman. But survives due to it being made from malfunctioning spare parts. Having earlier disabled the teleporter he is at a loss to explain how the Cyberman could have returned to the store so soon.

Cybermat Hunting

Returning to Craig’s home The Doctor works on the Cybermat while Craig looks after his son. The Doctor is then left alone with Alfie when Craig leaves to get some milk. Tending to Alfie's cries The Doctor is unaware that the Cybermat, that he had left downstairs, has become active. It attacks The Doctor and the returning Craig, but The Doctor manages to destroy it, by changing a setting on his sonic screwdriver, but not before it makes a mess of the house.

The following morning, The Doctor returns to the department store on his own with the reprogrammed Cybermat. Craig soon follows with Alfie. The Doctor then discovers that the Cyberman’ spaceship is not in space - but rather, it crashed on Earth centuries earlier and is now buried beneath the store. The Cybermen having created a secret tunnel whose entrance is in the department store’s changing room. The Doctor though is captured by the Cybermen and he learns from them that they are using power lines installed for the department store to supply power to their spaceship, and the crew of six plan to convert the entire human race when there is enough power.

Upstairs Craig, leaves Alfie with Val and follows The Doctor into the tunnel. However, as soon as he arrives he is captured and is placed in a conversion machine. The Doctor reveals his own impending death and urges Craig to fight, but the conversion appears to be complete - Alfie's cries can be heard over the closed-circuit television echo in the spaceship.

A Cyberman

The sound of his son in distress enables Craig to fight the conversion, sending the Cybermen into overload as they painfully feel the emotions they have repressed. Once free of the conversion machine and the Cybermen, The Doctor and Craig teleport away as the Cybermen’s spaceship explodes – the blast being contained by the underground cavern.

Back in the store Craig is reunited with Alfie as The Doctor slips away unseen. But when Craig returns home he finds that The Doctor has used the TARDIS’s time travel abilities to clean the mess from the previous night. The Doctor then leaves, just before Sophie returns, acquiring a set of ‘TARDIS blue’ envelopes from Sophie's stationery drawer and a Stetson hat from Craig – given to him as a parting gift.

With everything seemingly back to normal Craig tells Sophie that nothing out of the ordinary has happened, but Sophie becomes suspicious when the Alfie utters this first word: ‘Doctor’. Nearby, The Doctor tells the TARDIS this is their last trip and offers some parting words to a small group of children.

In the far future, River Song, a new Doctor of Archaeology, reviews eyewitness accounts by those children, and also notes the date and location of The Doctor's death. However, she is interrupted by Madame Kovarian and agents of The Silence. River Song is alarmed when Madame Kovarian tells her that she is still theirs, and will be the one to kill The Doctor. Despite her struggles they place her in an astronaut's suit and submerge her in the lake to await The Doctor’s arrival.