‘I thought the end of the world couldn’t get any worse.’ A routine episode that’s sharper than the first series, largely built around Nikki Amuka-Bird’s sympathetic central performance as the sleeper agent. Thematically, it begins where Doctor Who: Utopia ended: with a human revealed to be an alien monster in hiding (perhaps his experiences at the end of the universe have given Jack an extra-ruthless intensity when it comes to exposing the sleeper). From there, it goes down a different route, with Beth’s humanity not erased by the alien inside, but constantly struggling to reassert itself until the predictably tragic conclusion.

If you ignore the alien element, a lot of the episode plays like Spooks, with Beth brought into the Hub to be debriefed, brutally. Jack plays bad cop convincingly, taking her between an interrogation room and a cell, confronting her with a Weevil, and subjecting her to an intense, invasive scan that finally cracks through the shell and activates a grisly-looking implant. Gwen is the good cop, offering comfort and hope. Ianto offers sassy one-liners, Owen is a bit of a twat, and Tosh is competent. The main difference from Series One is that the team do all this without a lot of histrionic in-fighting, and when Owen suggests, ‘let’s all have sex’ it’s clearly a joke. The show is better for it.

The downside: once other sleeper agents are activated, the subtlety and mystery is abandoned in favour of some obvious and crass storytelling (the loving husband murders his wife; the paramedic walks away from doing CPR on a patient; the mother lets her pram roll in front of a car complete with off-screen crunch). The race to detonate nuclear missiles and destroy South Wales is the kind of thing that’s hard to play well in a mid-series episode, where the audience knows the stakes aren’t going to be that high, and as if to make up for it the direction and music suddenly become absurdly frenetic. In these sequences, too, the remaining sleeper’s arm-sword suddenly looks a bit rubbery and fake in medium shots. It pulls back for the denouement, but I think the dodgy climax means it’s a few steps away from being first rank.

Next Time: To the Last Man