Having been stuck with an Earth-only story format by the outgoing production team, Barry Letts and Terrance Dicks were left with the interesting question of how to get the Doctor into space again. An outright 180 at the start of Season 8 would have most likely been a bad idea, so instead we see a single outer space story among a season that's still otherwise earthbound. Commissioning Malcolm Hulke to write it was an interesting choice, but not necessarily a poor one. He manages to make a fun twist out of leading us to believe that it might be another "colony imperiled by aliens" story, before pulling the rug as we come to understand that IMC are the only real villains of the story.

Well, aside from the Master. His presence almost feels a bit incidental, but it is really funny how he reacts to the Doctor's presence, for the first time caught on the back foot because the Doctor wasn't supposed to be there for this particular scheme.

Although by no means remarkable, as a first sojourn into space for the Third Doctor this story is fairly good. I don't tend to think about it or rewatch it very often at all, but it does its job well.