Forget The Massacre: this is probably the most upsetting, disturbing episode of Doctor Who to date – perhaps ever. Because while The Massacre was rooted in the details of French religious warfare, this has all the immediacy of a war film, with the Doctor and his friends caught up, for the first time, in events that, in 1969, were in living memory of members of the audience.

Neither the script, by Terrance Dicks and Malcolm Hulke, or David Maloney’s direction pull any punches. Hulke and Dicks, in a very 1960s way, make this about the dehumanising machine of industrial warfare: once the Doctor, Jamie and Zoe are caught up in its cogs there is no escape for them, however much they protest their innocence. From the outset, the Doctor describes this as ‘one of the most terrible times on the planet Earth’, and seems unusually helpless in the face not of monsters or alien villains (so far as he knows), but small-minded human beings.

Troughton’s performance is almost too affecting: he plays this as though the Doctor knows he’s become snarled up in history; that his protestations will fall on deaf ears. Early on, he tries to keep Jamie and Zoe’s spirits up, but confronted by General Smythe and the power he represents, he’s reduced to shouting impotently, foreshadowing his fate right at the end of the serial. The little kiss he gives Zoe as he says, ‘Goodbye my dear’ is heartbreaking, and oddly reminiscent of Hartnell. And his lonely pacing in the condemned cell, awaiting dawn, is very moving. Hines and Padbury get slightly less to work with, but Hines’ comedy attempts to follow the Sergeant Major’s marching orders, and his brief show of defiance, conclude with him being physically lifted out of the room: this is not a situation Jamie can escape from.

Maloney’s direction, and Roger Cheveley’s design, sells all of this brilliantly. The film work is as strong as anything the show’s offered: the TARDIS materialising as a reflection in a puddle; the dynamic cuts as the shell barrage turns the wasteland into a confusing mess of explosions, as an ambulance crawls through the smoke. The sudden cut to frightening gas-masked soldiers is a Maloney hallmark (used again in Genesis of the Daleks and The Deadly Assassin). The staging of the Doctor’s execution looks like a documentary. This feels real. And the studio work is almost as strong, particularly the introduction of Smythe in a slow tracking shot, emphasising his isolation and power.

Given all this, the only thing that prevents this episode from being too horrible and upsetting for children is the early reveal that all is not as it appears. Characters are vague about dates and locations, and 10 minutes into the story Smythe reveals he has a futuristic TV in his room, and mentions the ‘1917 zone’. Later, he shows off his hypnotic glasses. This gives away a lot quite early, but I think it’s necessary: to leave us thinking this was all “real” would be sadistic. Instead, for all the awful grimness of the episode, we know this can’t be the end.

Next episode: The War Games – Episode Two