Parts: 4
Writer: Peter Grimwade
Airdates: 22 March 1982 - 30 March 1982
Production Code: 6C

Doctor: fifth
Companions: Nyssa, Tegan

Megalomaniac of the Week: the Master
Creature Feature: Plasmatons, Xeraphin

Story: En route from New York to London, a Concorde suddenly vanishes from English airspace over the Channel. Air traffic control is bewildered and panicked - what caused the plane to disappear, and how can they get it back? Their answer arrives in the form of the Doctor, who was en route to the Great Exhibition to cheer up Nyssa and Tegan when the TARDIS was forced into an early materialization. Once drafted into helping the Heathrow authorities, the Doctor requests that a second Concorde be sent along the same flight path as the first - but this time with the TARDIS and its crew aboard.

As the Doctor expects, the second Concorde encounters a time contour and begins travelling backwards along it. But he is bewildered when the aircraft receives landing confirmation from Heathrow - and then, when the Concorde smoothly touches down on tarmac, the passengers exit the plane to see present-day Heathrow outside. Yet Nyssa senses something wrong, and her intuition is confirmed when their surroundings prove to be an illusion. In fact, they have travelled back 140 million years in time, where they find the crew of the first Concorde under the delusion that they are in a New York airport.

These events have been masterminded by the mystic Kalid, who observes events from inside his citadel perched in the harsh Jurassic landscape. He is using the Concorde crew and passengers to help him breach the sanctum in the center of his citadel - but what is inside, and why is it so important? Aided by the officers of the second Concorde, the TARDIS crew must discover Kalid's secret and find out what lies inside the sanctum...for if Kalid gains control of it, he will possess the wisdom of the universe.