As the episode opens, Steven has returned to Anne believing that he has seen the Doctor’s dead body, and begins a desperate search for the TARDIS key in Preslin’s shop. At which point, without a word of explanation, the Doctor turns up, and it quickly becomes clear that he wasn’t impersonating the Abbot.

At which point the plot is functionally closed – the Doctor has no involvement in the events of the last two episodes, and, having found him, Steven has no need to remain in Paris. The only complication is Anne – who is quickly dismissed by the Doctor, to her likely death at her aunt’s house. Because, as the Queen Mother points out the next scene, she plans to unleash the mob, the ‘wolves of Paris’ (should have been the episode title), to kill all Huguenots in their midst. Tavannes’ disquiet at the horror he is unleashing is brilliant. But more disquieting is the fact that the Doctor doesn’t plan to lift a finger to help even one young woman escape it.

This is the endgame for the historical, and the philosophy that ‘you can’t change history: not one line.’ The Doctor will not contemplate amending even the smallest footnote (although 16 episodes earlier, faced with the same kind of scenario, the old hypocrite whisked Katarina away from Troy). Again and again he berates Steven – ‘I told you not to get involved’; ‘Please don’t interfere’; ‘I cannot change the course of history: you know that.’ Even after Steven rages at him, the Doctor’s refuses to provide any explanations beyond being ‘too small to realise [history’s] final pattern’.

There’s a hint of the later debate in Genesis of the Daleks – perhaps intervening in the great design in 1572 will mean than no good comes from this evil, and that the unintended consequences even of an act of mercy could change everything for the worse. But Bell of Doom forces the characters and the audience to contemplate whether that is a good enough answer. The slaughter in Paris is more dreadful on audio than it could have been on video – for 80 seconds we hear the screaming of the innocents, the shouting of the mob, the dolorous drums and the crackling of an inferno.

What was the point of any of this? Steven changed nothing. The Doctor absented himself from the story at every opportunity. Neither of them interact with most of the key players. There are three more historical stories to come, but they play more like fun adventures in great, gay costumes than any serious attempt to engage with their periods – and at the last, the next Doctor conspicuously does what this version won’t, and rescues one person from the clutches of history.

The Doctor again bemoans his inability to save anyone. ‘Oh, what a senseless waste,’ he says, having said much the same words over the ashes of Sara Kingdom. No wonder Steven leaves in disgust while the Doctor considers jacking it all in and going home.

But, as always, the TARDIS has taken the Doctor exactly where he needs to go. Suddenly, in walks Dodo, who shares with Anne not only a surname but a family background (she lives with her aunt), closely followed by Steven. She quickly lifts the mood with her cheeky Northern impudence:

STEVEN: How did you get in here?

DODO: On me feet, same as you did!

However unlikely, it seems that Anne almost certaintly escaped the massacre – proving the Doctor’s point that time (and TV show production) works in mysterious ways, and taking Anne as a new companion would have prevented Dodo from ever existing. Out of the evil, something has come good.

And as the TARDIS and its new crew fly away for new adventures, we try to put from our minds the poor, injured little boy lying on Wimbledon Common: the final tiny victim of the Doctor’s refusal to interfere.

Next episode: The Steel Sky