Parts: 4
Writer: John Flanagan, Andrew McCulloch
Airdates: 27 September 1980 - 18 October 1980
Production Code: 5Q

Doctor: fourth
Companions: the second Romana, K-9 mark two

Megalomaniac of the Week: Meglos

Story: Since they happen to be passing by, the Doctor decides to pay a visit to his old friend Zastor on the planet Tigella. Even as they are on their way, a fierce debate is raging on the planet. Years ago, the surface - covered in lush and aggressive vegetation - had been deemed inhospitable by the inhabitants. They retreated underground to live with the aid of the Dodecahedron, a source of immense power and worshipped by some of the Tigellans. But now the power is failing, and the less reverent Tigellans feel it would be wise to move back to the surface.

Meanwhile, a band of Gaztak raiders bring a lone Earthman to the nearby planet of Zolfa-Thura. They are met there by Meglos, a cactus-like creature who needs to control the Earthman's body for greater mobility. That achieved, he intends to go to Tigella to retrieve the Dodecahedron...but first, he must get the Doctor out of the way. To that end, he traps the Doctor, Romana and K-9 in a neverending time loop...

Taking on the Doctor's appearance, Meglos infiltrates Tigella and gains entrance to the revered power room where the Dodecahedron is held. The next the Tigellans know, their precious energy source and god has been stolen. Meglos intends to use the Dodecahedron to access reserves of incredible power...and with that power, he will have domination over the entire universe...