The Daleks have developed ridimentary time travel and are after the Doctor so that they may capture his TARDIS and learn more advanced ways of time travel. They TARDIS crew are chased throughout the cosmos having to avoid several threats other that the Daleks along the way. The crew end up on a planet populated by the Mechanoids and meet Steven, the only survivor of a wrecked space craft. The Daleks and Mechanoids destroy each other and Barbara and Ian use the surviving Dalek time machine to journey back to Earth in 1965. Steven remains with the Doctor and Vicki.