First broadcast 20 September 1986.

Captured by the Tribe of the Free, the Doctor (Colin Baker) strives in vain to convince Queen Katryca (Joan Sims) to shut down the black light generator powering the robot Drathro (Roger Brierley). When the generator is not shut down but destroyed, it triggers a crisis that could kill everyone on Ravalox.

For the most part, the third instalment of the “Mysterious Planet” storyline suffers from much of the same problems most old Doctor Who third parts have. There is too little plot to sustain a full 25 minutes of action, and as a result far too much getting captured, getting freed, and running around. One of the smartest things the production team implements from the following year is three-part stories.

What plot there is turns out to be very welcome. References to mysterious ‘sleepers’ from the Andromeda galaxy, some kind of intergalactic conspiracy, and stolen alien technology provide a level of complexity and intrigue that the first two episodes lacked. When elements of the footage during the Doctor’s trial are unexpectedly redacted, it ties the events of the trial to the events on Ravalox properly for the first time.

The Tribe of the Free, who have struggled to convince since the beginning, become fairly untenable at this point. Joan Sims is not believable as a strong-willed dark ages queen, nor it must be said is David Rodigan as her right-hand support Broken Tooth. When the tribe masses together, such as they are, on a mission to invade Drathro’s underground base, they could not feel less like a warrior tribe. An amateur dramatic troupe easily comes to mind.

Doctor Who was a cheap series to make, and stereotypical jokes about wobbly sets and washing-up bottle spaceships were tiresome at the time. What could override the series’ technical limitations were good writing and committed performances. While the scripts by Robert Holmes hold up for the most part, it constantly feels like the actors – the extras in particular – simply do not have their heart in it. They are letting the episode down.

It is also worth noting that, for a series based around cliffhanger endings every half hour, the climaxes of these first three episodes have all been relatively weak. By the end of this first serial of the year, fully half of the cliffhangers will have been close-ups of Colin Baker looking shocked.