The Doctor is apprehended by the Moroks, who control Xeros. Meanwhile, the native Xerons plan a revolution against the Moroks.
Unlike most other fans, I believe "The Dimensions of Time" is just as good as the opening episode. It's a fun episode, and while there's bad bits, the good outweighs the bad.
We are introduced to both the Moroks and Xerons this episode. The Xerons are Tor (Jeremy Bulloch), Sita (Peter Sanders) and Dako (Peter Craze, brother of Michael). Bulloch comes of the best, while Craze is a bit rough. However, Sanders is truly horrendous, delivering is lines without any conviction whatsoever. The Xerons are appallingly badly written though, and saddled with lines like "One minute it was silence, the next minute a whirlwind hit me!". The Morok actors fare a bit better. Richard Shaw, as Lobos, is the only one who gets a lot of lines, and he's competent enough.
William Russell, Jacqueline Hill and Maureen O'Brien spend the episode wandering around the drab museum sets; we do get the hilarious sight of William Russell trying to tear a cardigan apart with his teeth though.
The main pleasure of the episode is William Hartnell. He's on top form this week, and the script gives him plenty to work with. The scene where he hides in a Dalek is classic, but my favorite bit is his interrogation by Lobos at the end. Hartnell really is delightful.