The final segment of the Key is traced to the planet Atrios, engaged in a long war with the Zeons.

The Doctor and a newly-regenerated Romana arrive on Skaro and discover that the Daleks are using explosive charges and a group of humanoid slave workers to mine the planet in search of their creator, Davros. A stalemate has arisen in an interplanetary war that the Daleks are waging against the robotic Movellans, and their hope is that Davros will be able to give them the edge.

The TARDIS is temporarily captured by the Mandragora Helix, a spiral of energy with a controlling influence, at the centre of which the ship is infiltrated by a sparkling ball of energy.

The Doctor locates the first segment of the Key to Time, but can't release it. Unstoffe: Nigel Plaskitt. Romana: Mary Tamm. Garron: Iain Cuthbertson. Graff Vynda-K: Paul Seed.

The Doctor discovers a planet that has been hollowed out so that it can transmat through space.

The Doctor encounters a living energy structure known as the Mandragora Helix in 15th century Italy. Now he must fight against a sinister cult with plans to use the Mandragora to swallow up the moon and enslave all of mankind.

The TARDIS arrives on contemporary Earth, where Sarah comes into contact with what appears to be a fossilised human hand - the last surviving fragment of a murderous alien called Eldrad.

On Skaro, Doctor Who and Romana (Lalla Ward) encounter their archenemies---the Daleks. Tyssan: Tim Barlow. Cmdr. Sharrel: Peter Straker. Agella: Suzanne Danielle. Lan: Toby Osoba. Veldan: David Yip.

Earth faces an invasion of Autons armed with deadly plastic daffodils and led by Dr. Who's archenemy, The Master (Roger Delgado). Dr. Who: Jon Pertwee. Jo Grant: Katy Manning.

The Doctor matches wits with a mind-controlling machine that contains an evil alien parasite. Jo: Katy Manning. The Master: Roger Delgado. Brigadier: Nicholas Courtney.

The Doctor investigates the disappearance of the advanced aircraft Speedbird Concorde. Peter Davison, Sarah Sutton. Hayter: Nigel Stock. Tegan: Janet Fielding. Stapley: Richard Easton. Sheard: Brian McDermott.

The Doctor battles the Master and a renegade Time Lady named Rani, who are wreaking havoc on a 19th-century mining community. The Master: Anthony Ainley. Peri: Nicola Bryant. Jack Ward: Peter Childs.