What's the rating?

Wiped.

What's interesting about it?

The departure of Steven, apparently to the surprise of all, including actor Peter Purves, who would go on to be a member of the Blue Peter crew. Steven is left to be the benevolent ruler of a planet, somewhat against his will. In an interview, Purves says he always thought the show should return to the planet sometime to discover he'd become a despot. No one has taken him up on this.