Assisted by the argumentative Romanadvoratrelundar and K9, he lands on the planet Ribos in search of the first segment and finds himself entagled in the machinations of two sinister strangers, Garron and the Graff Vynda Ka.

Who are they? Is Garron simply a shady confidence-trickster dealing in interplanetary real estate? Is the Graff Vynda Ka just a power-crazed exil bent on revenge? Or are they oth really agents of the Black Guardian, intent upon seizing the precious Key in order to throw the Universe into eternal chaos?

Risking his life within the monster-indested catacombs of Ribos, the Doctor has to use all his wit and ingenuity to find out ...
 

The Doctor and K9 Mark II are sent on a mission by the immensely powerful White Guardian. The six segments of the Key to Time, currently disguised and scattered throughout the cosmos, need to be brought together. Once assembled, the Key will allow the Guardian to restore balance and good to a universe that is descending into evil and chaos. It will also thwart the plans of the fearsome Black Guardian! As if accepting such a daunting task wasn't enough, the Guardian appoints a new young assistant for the Doctor, Romanadvoratrelundar - or Romana for short.

Fresh out of the Time Lord Academy, the 140-year-old Romana is confident that their mission will be easy and, if the Doctor can curb his irrational behaviour, can be rapidly completed. Using a special Tracer, the TARDIS locates the first segment on the feudal planet Ribos, where two inter-galactic criminals are using a lump of Jethryk as bait in a plot to trick a visiting nobleman into buying the planet - which is not theirs to sell. The Doctor finds himself drawn into the con-men's fiendish plan while Romana has to confront the monstrous Shrievenzale...

Running Time: 99 mins approx
Original transmission date: 2nd September 1978 to 23rd September 1978
Produced by Graham Williams
Directed by George Spenton-Foster