The best thing about this one is all the aliens - Chumblies, Drahvins and Rills. Having them fight it out between them with the Doctor, Steven and Vicki getting caught in the middle is very entertaining. As always, it was the non-missing episode (found in 2011) that I enjoyed the most, so it's very difficult to judge this one fairly.

I found Steven in the airlock suffocating to be the best thing about the story - brilliantly acted. Oh, and what a cliffhanger!