UNIT is called in when an important diplomat is attacked in his own home - by a man who then vanishes into thin air. The Doctor and Jo spend a night in the 'haunted' house and meet the attackers - who have time-jumped back from the 22nd century in the hope of changing history.Travelling forward in time, the Doctor and Jo find themselves trapped in a future world where humans are slaves and the Daleks have already invaded. Using their ape-like servants to Ogrons to maintain order, the Daleks are now the masters of Earth.As the Doctor desperately works to discover what has happened to put history off-track, the Daleks plan a time-jump attack on the 20th century.This novel is based on a Doctor Who story which was originally broadcast from 1 to 22 January 1972.Featuring the Third Doctor as played by Jon Pertwee, with his companion Jo Grant and the UNIT organisation commanded by Brigadier Lethbridge-Stewart