The TARDIS lands in London on Christmas Eve, 1851 and almost immediately the Doctor hears his name being called. When he meets the woman shouting for him she fails to recognise him and continues calling until another man arrives and claims to be the Doctor and acknowledges the woman, Rosita, as his companion. The Doctor then attempts to help the newcomer lasso a man-size dog-like creature which has a cyber-mask, but it drags them both through the upper floor of a warehouse until Rosita cuts the rope, saving them both from plunging through a high window. The newcomer explains he has lost his memory, and the Doctor assumes he is a later incarnation, and follows him to the house of a murdered vicar, where the new Doctor says he is investigating the murder of the vicar and a teacher called Jackson Lake, and that his memory was wiped when he was attacked by the Cybermen. At the house the Doctor finds primitive memory devices called infostamps and says they have been used by the Cybermen bec ...