On the planet Tigella, the mysterious source of all power, the Dodecahedron, is failing.  So Zastor, the leader of the planet, decides to call on an old friend - who travels the universe in a blue police box - to help them.  Meanwhile, on the nearby dead planet of Zolfa-Thura, a rag-tag band of space raiders form an uneasy alliance with the cactus-like alien Meglos.

Their first goal is to prevent the Time Lord from arriving on Tigella.  Aboard the TARDIS, the Doctor, Romana and K9 find themselves trapped in a Chronic Hysterisis - a time loop that keeps them endlessly repeating the same few moments in time, again and again and again.  Double trouble awaits them if they ever manage to reach Tigella...

Starring Tom Baker as the Doctor / Meglos,
Lalla Ward as Romana and John Leeson as the voice of K9. 
Also features Jacqueline Hill (companion Barbara from first two seasons of Dr. Who) as high priestess Lexa.

BBC, Color, 1980. 

Runtime approx. 87 mins.