The Daleks (Gerald Taylor, Robert Jewell, Kevin Manser, John Scott Martin; voiced by Peter Hawkins, David Graham) have constructed a time machine, and an execution squad is dispatched to pursue and kill the Doctor.

The chase begins on the desert planet Aridius, where the travellers encounter ferocious Mire Beasts (Jack Pitt) and narrowly avoid being handed over to the Daleks by the native Aridians, led by Malsan (Ian Thompson), Rynian (Hywel Bennett) and Prondyn (Al Raymond). It then takes in such stopping-off points as the top of the Empire State Building, the 19th-century sailing ship Mary Celeste - the Daleks' appearance causing all the crew and passengers to jump overboard - and a spooky haunted house which, although the Doctor and his friends do not realise it, is actually a futuristic funfair attraction, Frankenstein's House of Horrors, at the Festival of Ghana in 1996.

Eventually the action moves to the planet Mechanus, where the travellers are taken prisoner by the Mechanoids (Murphy Grumbar, Jack Pitt, John Scott Martin, Ken Tyllson). A fellow prisoner, Steven Taylor (Peter Purves), tells them that the Mechanoids are a group of robots sent some 50 years earlier to prepare landing sites for human colonists who, in the event, never arrived. At the story's climax, the Daleks and the Mechanoids engage in a fierce battle which ultimately results in their mutual destruction. As the city burns behind them, the Doctor's party seize this opportunity to escape and return to the TARDIS. Steven Taylor also manages to get away.

Ian and Barbara realise that they can use the Daleks' now-abandoned time machine to return to 20th-century Earth and, once his initial objections have died down, the Doctor helps them to do so. The two friends are delighted to be back home, although they quickly realise that they have arrived in 1965, two years later than when they left, leaving them with the difficulty of explaining their long absence!

_{Synopsis from Doctor Who: The First Doctor Handbook by David J. Howe, Mark Stammers and Stephen James Walker, reprinted with permission; further reproduction is not permitted. Available from Telos}