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.