Two RAF fighter jets are on a training flight over Northeast Scotland when one of them is plucked from the air and promptly disappears. UNIT are called in, and the Doctor and Brigadier Lethbridge-Stewart are soon on the scene. They enlist the help of a local military officer - a young lieutenant by the name of Mike Yates. The Doctor discovers a link to the recumbent stone circles that are plentiful in this part of Scotland. The stones are thousands of years old and are soon revealed to hold a terrible secret.

Responding to a desperate summons from the Doctor's future self, he and Peri find themselves on a sailing ship in 1492, where the crewmen are gripped by superstitious fear. They say the Devil walks among them, stalking and striking them down. Even though they have landed in paradise, they fear that 'El Diablo' himself will drag them over the edge of the world and into the depths of Hell.

In the far future, the inhabitants of Tarsus Six face a desperate struggle to evacuate their world before their sun, Tarsus Ultra, collapses into a cataclysmic spatial anomaly. When the Doctor navigates the Tardis to a space station orbiting Tarsus Six, Ace assumes that he intends offer their assistance. But it soon becomes clear that the Doctor has an agenda of his own. With the Tardis immobilised, Ace realises that their own lives are as much in danger as those of the fleeing inhabitants.

The Doctor answers a psionic distress call being sent from England in the 1920s. There, in the environs of a fairground, he is reunited with an old friend: Harry Houdini. To Adric and Nyssa the name means very little, but to the Doctor's companion, Tegan, he is a legend. An escape artist extraordinaire, Houdini's reputation will last for decades. But how does Harry knows so much about Tegan?

Nineteen thirty-five: a message from a Time Lord in trouble sends the Eighth Doctor and Charlotte 'Charley' Pollard to the streets of London's West End, in search of a mysterious alien adversary - unaware that something monstrous is already on their trail. They soon discover that an insidious conspiracy is indeed at work, its tentacles extending the length of the British Isles.