After an encounter with a hostile robot called a Chumblie, the Doctor and his companions are rescued by a group of female Drahvins.

With the knowledge that the planet will be destroyed in two days, the Drahvins instruct the Doctor to help them steal the Rills' ship.

The Doctor and Vicki encounter the Rills and learn the situation is more complex than they thought while Steven finds the Drahvins' hospitality ever more perilous.

The Doctor and Vicki enlist the aid of the Chumblies to rescue Steven from the Drahvins and then find a way off the planet before its destruction.

Space Security agent Marc Cory visits the planet Kembel to investigate rumours of Dalek activity in the area. However, his ship is shot down and his crewmates are poisoned by the thorns of Varga plants, genetically engineered carnivores which transform their unlucky victims into Vargas as well. Despite these dangers, Cory discovers that the Daleks have formed an alliance with several other alien species, intending to launch a war against Earth. He makes a tape of his discoveries -- but is exterminated before he can get word to his superiors...

The Doctor infiltrates the Daleks' conference to try and discover their plans, leaving Steven, Katarina and Bret to find a way off the planet.

The Doctor, Steven and Sara are accidentally transported to the planet Mira where Chen sends the Daleks after them.

The Doctor, Steven and Sara travel to Ancient Egypt, pursued by both the Daleks and the Meddling Monk.

The Doctor, Steven and Dodo arrive on a giant spaceship millions of years in the future, transporting the last humans away from the doomed Earth.

With the Ark infected with a cold virus, the Doctor must convince the Guardians to trust him so he can find a cure.

The Doctor, Steven and Dodo have travelled 700 years into the future and find that the Ark is now under the control of the Monoids as it approaches Refusis.

The Monoids abandon the Ark, leaving Steven and the Guardians to die, but a mutiny in their ranks may give the Doctor a chance to bring about peace.

As the Doctor nears the end of his game against the Toymaker, Steven and Dodo take on Cyril in a lethal game of hopscotch to try and recover the TARDIS.

The TARDIS arrives in Tombstone, Arizona in 1891. Where the Doctor is looking for a dentist when he has a toothache, where The Doctor finds the local dentist is the famous Doc Holliday who is in a feud with The Clanton Brothers and their hired gunfighter Johnny Ringo, whilst local sheriff Wyatt Earp is trying to keep the peace. The Doctor, Steven and Dodo find themselves joining forces with The Clanton Brothers and Sheriff Wyatt Earp.

With the Clantons believing the Doctor to be Doc Holliday, Wyatt Earp takes him into protective custody but this leaves Steven and Dodo in danger.

Earp comes to Steven's rescue and arrests Phineas Clanton, prompting the Clantons to decide to enlist the help of Johnny Ringo.

The Clantons have shot Warren Earp, leading to a showdown between the two families with the Doctor powerless to prevent bloodshed.

The Doctor and Dodo return to London in the present day where the Doctor becomes concerned about WOTAN, a new super-computer installed in the Post Officer Tower.

Dodo is under the control of WOTAN and attempts to lure the Doctor into a trap, while the rest of WOTAN's slaves begin construction on its robotic War Machines.

Ben tries to escape from the warehouse but is captured by Polly, who is now also under WOTAN's control, and forced to work on construction the War Machine.

London 1966 and the Doctor and Dodo, on a visit to the Post Office Tower, meet Professor Brett whose new computer WOTAN can actually think for itself and is soon to be networked with other computers around the world. However, WOTAN believes that humans are inferior to machines and should, therefore, be ruled by them. Exerting a hypnotic influence, WOTAN arranges for the construction of War Machines - heavily-armed, self-contained mobile computers - with which to take over the world. These prove more than a match for the Army, but the Doctor is able to capture one of them, which he then re-programs to destroy WOTAN. When the crisis is over, Dodo chooses to remain in London; Ben and Polly, however, inadvertently become the Doctor's new companions when they enter the TARDIS to return his lost key.