“Retrocausation! Events before their cause. Time in reverse.”

While investigating a temporal anomaly in Central London, the Doctor and Jo Grant meet Professor Harold Saunders, a man who possesses an unstable alien artefact, and who is seemingly haunted by the ghosts of dolls.

Who is the mysterious Mrs Killebrew? Why is a pack of hounds hunting them in reverse? And can Jo pick up any bargains while backwards shopping on Oxford Street?