Sarah Jane tells Maria and Luke about a meteorite on course with Earth but reassures them that Mr Smith will be able to deflect it the following day. Sarah Jane gives Maria an alien puzzle box to cheer her up; she falls asleep that night holding it, as a mysterious cloaked figure approaches Sarah Jane's house. The next day, Maria finds that Sarah Jane, Luke and Mr. Smith have all disappeared, and she alone remembers them. A woman named Andrea Yates is living in Sarah Jane's house.
Investigating, Maria finds a 1964 newspaper report stating that a thirteen-year-old Sarah Jane Smith drowned after falling from a pier, where she was playing with her friend Andrea Yates. As Maria watches, the names of the deceased and the survivor keep switching. When Maria confronts Andrea, the panic stricken woman rushes to her attic and finds a second puzzle box. The cloaked figure appears and offers to make Maria disappear. After Andrea accepts, he dispatches a Graske, who captures Maria just after Alan picks up the first puzzle box. When Chrissie comes round he discovers his ex-wife cannot remember their daughter. Meanwhile Maria escapes from the Graske and finds herself on a beach promenade near two girls. They introduce themselves as Andrea and Sarah Jane Smith.
After failing to dissuade Andrea from taking Sarah Jane to the pier, Maria is recaptured and taken to join Sarah Jane on a white misty plain, limbo. The mysterious figure explains he has removed Sarah Jane from Earth's timeline so the meteorite will destroy it and create the chaos on which he feeds; the Doctor will be his next target.
Alan accompanies Chrissie to Andrea's birthday party. Remembering Maria's suspicions, he questions Andrea, who takes him to the attic and tearfully reveals the truth. When she fell off the pier and Sarah Jane was unable to save her, a voice offered to switch the girls' places, and she accepted. The figure appeared and gave her the puzzle box, then removed himself from Andrea's memory; Maria’s questions made Andrea remember. Alan is now chased into the street by the Graske but knocks it down and ties it up, then uses its device to bring back Maria.
They return to the attic, where Sarah Jane appears in the mirror and explains to Andrea that witnessing her death gave her the resolve to fight pointless deaths herself. When the figure reappears (called “the Trickster” by Alan), Andrea explains she has changed her mind about the deal and throws her puzzle box at the mirror, smashing both. Back in 1964 Andrea falls to her death, while Sarah and Luke reappear in the attic and activate Mr Smith. The party guests, including Clyde and Chrissie, have learnt from television news about the incoming meteorite, and are relieved to see it suddenly diverted from its fall. The episode ends with Alan demanding an explanation of his daughter’s involvement with aliens and supercomputers.
Elisabeth Sladen – Sarah Jane Smith
Yasmin Paige – Maria Jackson
Tommy Knight – Luke Smith
Daniel Anthony – Clyde Langer
Alexander Armstrong – Mr Smith
Joseph Millson – Alan Jackson
Juliet Cowan – Chrissie Jackson
Jane Asher – Andrea Yates
Jimmy Vee – The Graske
Paul Marc Davis – The Trickster
Jessica Ashworth – Young Sarah Jane Smith
Francesca Miller – Young Andrea Yates
Writer Gareth Roberts
Director Graeme Harper
Script editor Lindsey Alford
Producer Matthew Bouch
Executive producer(s) Phil Collinson
Russell T. Davies
Series Series 1
Length 2 episodes, 25 mins each
Originally broadcast 29 October & 5 November 2007