After the doom and gloom of the last six weeks, this is a fantastic breath of fresh air. The opening is excellent: toucans and lizards hopping about a jungle, disturbed by the approach of an alien creature – the camera pans across and the TARDIS arrives. Out comes Dodo, full of beans, followed by a very grumpy Steven – both unaware of the alien creature stalking the forest.

Somewhere else, a futuristic court condemns a man to miniaturisation for carelessness, establishing the harsh justice in this world. The connection between the hi-tech courtroom and the jungle is established by the presence of the Monoids in both – and it’s clear they aren’t quite the alien monsters they initially seemed to be, as they’re apparently working in harmony with the humans.

Back in the jungle we get our first proper scenes with Dodo. She’s feckless and impetuous where Steven is cautious – and a lot less Northern this week. She also seems to irritate both the Doctor and Steven, although she still gets the best line in the episode:

STEVEN: Are you crying?

DODO: No, me nose is running!

The scale of the episode is spectacular: a real life elephant; a jungle inside a spaceship; the end of the Earth; a 700-year journey to Refusis Two, and segments of time measured in millions of years. The casual revelation that humanity has left the Earth for the last time is stunning (and we assume a few million miles away the Ninth Doctor and Rose are watching EarthDeath on Platform One). It’s proper Golden Age of Sci-Fi stuff. But there’s also some commitment to genuine science: the Doctor trying to infer their location from the facts he can see – a roof where there should be sky, and the mechanical vibration of the earth under his hand (in a scene lifted for The Beast Below).

There’s also a commitment to making this feel like a real place – the Guardians proudly showing off their generation ship, including its miniaturisation banks containing millions of refugees, and the great statue that’s the centrepiece of their community. The Monoids use sign language, and drive around in gear Chockablock carts.

Into this paradise Dodo has brought coronavirus, which humanity eliminated generations ago and to which it now has no immunity. This all seemed laughable just a few months ago, but the deadly spread of a nasty cold through a terrified population now seems chillingly believable.

Aside from very weird performances by Eric Elliott as the Commander and Inigo Jackson as Zentos, and the description of the TARDIS as a ‘black box’, this is really good – a genuine sense of peril, and a central role for the time travellers.

Next episode: The Plague