With everything beginning to converge back on Skybase, this episode is largely about spinning plates for a week. Not a huge amount of new information is disclosed, not a great deal happens, it’s another fifth episode that feels like it’s marking time.

There’s definitely a nod towards upping the ante. It turns out all of Jaeger’s terraforming rockets malfunctioned, and instead of converting the atmosphere they’ve spread their payloads on the surface of Solos, which will ultimately render the entire planet uninhabitable. Without the Doctor’s assistance to complete particle reversal, everything will die. The Marshal, caught in the increasing convolutions of his own tangled web of deception, holds Jo and Ky as hostages to compel the Doctor to help (as if he’d have refused to prevent genocide). Everyone waits with bated breath for the Earth investigator to turn up.

Really, this is very routine. There’s some effort to inject a bit of fun – the Marshal gets a good line (he replies, ‘Only if I lose’ when the Doctor accuses him of madness), and there’s some business with the sonic screwdriver (‘And the other thing,’ says a guard when confiscating it from the Doctor – a line repeated by Jo a few minutes later when she frees herself). The Doctor’s wittering about anti-matter turning everyone into un-people points the way to the central idea of the writers’ next serial, The Three Doctors. Sondergaard’s meeting with the chittering Mutts is another example of this era taking a more nuanced approach to its monsters than the last one.

Next episode: The Mutants – Episode Six