It is Victorian London and Jack the Ripper is stalking the streets -- or is it the Doctor?A crystal from the TARDIS' telepathic circuits has a serious effect on the Doctor's mind, and Ace finds herself isolated and in danger.What part is the Doctor being forced to play? What is the secret of the 12 shadow-TARDISes which eerily wait in silence for events to play out? Only as Ace runs for her life does she realize that the Doctor is at the mercy of a terrifying force from his own future -- one he may be powerless to stop.