‘They’re all safe, aren’t they? The children, the grandchildren. Everyone’s safe?’ After the set-up of Human Nature, the first half of this episode is almost relentless action as the Family and their scarecrow army attack the school and Smith mobilises the boys into a makeshift fighting force to the disgust of Joan. Given the emotional heft of the back half of the episode, it’s easy to overlook the power of these sequences. The Headmaster’s stand-off with Son of Mine, a threat he doesn’t understand and can’t conceive the enormity of, is superb. Son of Mine carries the knowledge of the wars to come, and the Headmaster can’t stand against the entire weight of history. The scene of terrified children machine gunning scarecrows to pieces is a horrible analogy for what is going to happen to them in just a few years.

It sets the scene for an episode about the nature of sacrifice, laying down your life for people you’ve never met. Smith’s revulsion at the idea of the Doctor, the possibility of a long and happy life with Joan, is offset against ‘war across the stars for every child’. In the end, Martha’s appeals for Smith to become the Doctor because she loves him and it was always meant to be are basically irrelevant to Smith’s decision. It’s Joan’s appeal to his duty of care to the children, first at the school and then basically everywhere that makes the difference. Under Moffat, the series often returns to this idea of the Doctor as protector of children. While the Family of Blood are equally committed to making sacrifices for their own Son of Mine: ‘This is all for you so that you can live forever’, theirs is motivated by selfishness not Smith’s final, literal selflessness. Arguably, the Remembrance Day service at the end labours the point, but I think seeing an elderly Tim having enjoyed a long life is the pay-off to the earlier flash forward to an aged Smith: he died, but Tim lived, there’s balance.

The whole piece lives or dies on the relationship between Smith and Joan. Tennant’s performance didn’t need to be his strongest so far, but the fact that it is lifts this towards greatness. Smith is a tangibly different performance from the Doctor, which shines through in the scenes when he flips between the two (especially when he slips into Doctorese when Tim hands him the watch). But for me, the greatest moment is his reaction when Joan asks the Doctor the killer question: ‘If the Doctor had never visited us, if he’d never chosen this place on a whim, would anybody here have died?’ Tennant’s eyes harden as the Doctor realises how much Joan, ever so politely, hates him.

Jessica Hynes is brilliant as well, beautifully playing Joan’s public and private faces. I love the way she clings to the journal whenever Martha and Smith’s arguments start to get heated, as she represses her own emotions in a very period-appropriate way. I also admire Cornell and RTD for making her spout the racist views of her time, rather than writing her as an impossibly perfect anachronism.

It’s a masterpiece, then. Like the Dalek Emperor using the Human Factor to help define the Dalek Factor, it makes Smith’s incipient pacifism, bravery, basic decency and floundering humanity highlight the Doctor’s defining traits. The major difference is the pitiless punishment of the Family, putting on screen the often promised but rarely shown ‘no second chances’ side to the tenth Doctor. Sitting right at the middle of Tennant’s run, this might just be his definitive story. Should have called this episode Love and War, though.

Next Time: Blink