The episode begins with a fairly weighty discussion on the morality of time travel, and the possibility that the TARDIS has been spreading deadly germs throughout time and space. ‘I don’t want to think about it, it’s too horrifying,’ says the Doctor, closing down any further discussion. So the question is never resolved. To an extent, it’s slightly pointless to raise such a significant idea only to leave it hanging, and I wonder if it’s part of an effort by Wiles and Tosh to question the ethics of the Doctor’s travels. As with The Family of Blood 40 years later, the audience is asked to consider if the Doctor didn’t land here, on a whim, would anybody have died? Neither Wiles nor RTD has an easy answer, but it’s clearly an idea that’s unsettled generations of producers.

At least the Doctor seems genuinely crushed when one of the Guardians dies, and is eager to volunteer his services finding a vaccine. In the meantime, the Guardians adopt some safety measures, like fancy face masks (modelled by Michael Sheard in his first Doctor Who appearance), but not social distancing or enforced lockdowns. The race for a cure is fairly basic sci-fi stuff, and the episode hilariously cuts away before Hartnell has to explain any of the science of the virus, but he does get the best line:

DOCTOR: I know I’m a bit of a quack.

As in The Steel Sky, there’s a sustained effort to make this future feel like a real place, with an off-hand reference to knowledge lost in the Primal Wars of the 10th Segment, and a sequence of a Monoid funeral march (that Dodo savagely describes as ‘sounding like savages’), and the consigning of the dead into the void of space. All this reinforces the horror of what is happening, and its impact on the community.

Less impressive is another of Doctor Who‘s occasional futuristic trials, in which the judge is horribly partial. Zentos sounds like one of the dads watching the show, scoffing ‘as if’: ‘Do you expect us to believe that nonsense? That you manage [to travel through time] in that ridiculous machine called the TARDIS?’

All comes good in the end, though. For the first time in what feels like a long time the Doctor comes good, and saves the last of humanity as the Earth dies in a ball of flame. It’s one of his most rousing triumphs, and so his little homily to a repentant Zentos – ‘Travel with understanding as well as hope’ – feels earned. And with that, the time travellers bid goodbye to the last humans (Dodo’s little wave to their Monoid driver is lovely) and they go on their way.

The Ark is a very slight story, but it’s a decent attempt to create a future world in a way that’s going to become increasingly rare. And it raises some interesting questions about the morality of the Doctor’s travels without finishing in darkness – the first happy ending, in fact, since The Exploding Planet‘s.

But what’s this? The TARDIS has landed back in the same place? And the Monoids have taken over?!

Next episode: The Return