The Doctor and his own Holly Goodhead, Nurse Pinto, have infiltrated the Chameleon space station as the alien master plan approaches its conclusion. As above, so below: on earth the Commandant, Jean and Sam are desperately searching for the comatose bodies of the Chameleons’ victims.

What this results in is a series of phone calls between Earth and space, and some location filming in Gatwick Airport car park. The Doctor sowing seeds of dissent between the elite Chameleons, whose originals are stowed in space, and the grunts who are relying on no-one finding their originals at Gatwick Airport. This all seems a bit dim: why not just make everyone safe on board? The originals are bound to be found eventually, which will presumably mean the end for their doppelgangers.

This plays out first in ponderous slow motion and then a sudden change of heart, given the Chameleons are a dying people and this is their chance for survival. While the Doctor causing chaos, damaging the conversion unit, is hugely fun, his bargain with the Chameleons makes almost no sense – sending them packing to their possible extinction without any fuss or recrimination. No wonder the Commandant is so cool about the whole affair:

COMMANDANT: Flap over. Let’s get back to normal as quick as we can

The final few minutes are a series of goodbyes – the Commandant bids farewell to ‘Scotty’, Sam gives Jamie a ‘ta-ra’ kiss, and then Ben and Polly realise they’ve got home – Ben can go and be an admiral and Polly can be his carer. At least they get an onscreen farewell, unlike Dodo – but it’s not a lingering one: someone has stolen the TARDIS.

Like this story, Ben and Polly seem to gradually fizzle out. They were genuinely refreshing when paired with Hartnell, but since Troughton took over (and Hines joined) their roles have been less and less interesting. Partly this is the inevitable result of a crowded TARDIS – even the first Doctor slimmed down to two crew after Ian and Barbara left. But I think while their brashly contemporary style was an interesting contrast to Hartnell’s Doctor, it works less well with Troughton’s. In the historical stories, Ben and Polly could seem almost cruel to their ignorant ancestors (mocking their superstitions and customs), and with a more active, bafflegab-ready Doctor, their usefulness in the outer-space stories was significantly reduced. Their replacement with the softer, simpler Jamie and Victoria, taken alongside the toning down of the second Doctor’s more unnerving tendencies, perhaps represent a more child-friendly approach.

Next episode: The Evil of the Daleks