Collision Course. Season 1, Episode 3. First broadcast Thursday 18 September 1975.

Moonbase Alpha is on a collision course this week, ineluctably destined to crash into a giant pustulent planet. Or is it? Commander Koenig — overcome by the charms of Queen Margaret Leighton — doesn’t think so, and so he turns up to Main Mission in his pyjamas like a Moonie and threatens to gun down anyone who attempts to prevent the collision, including, upsettingly, our own Barbara. But — inevitably — it all turns out for the best, and we end our second episode in a row staring out the window contemplating the metaphysical metamorphosis we have wrought.