Episode 1

The season opens in the shadow of the hotel explosion, with Section D doing what it does after a loss: asking what the work costs, and then going back to work anyway. The new target is a boat crossing from Tangier, carrying Abib, a Somalian AQ terrorist, and a load that turns out to be lethal. The obvious destination is Plymouth, where the Royal Navy is launching its newest ship, and the episode spends a while letting the team chase that obvious answer.

The trick is in the question it keeps raising: whether the real target is elsewhere, and whether there is still time to find the UK source of the plan. Meanwhile Lucas is visited by an unwelcome ghost from his past, and his faith in the job takes a knock. The two strands never quite touch, and the hour is better for keeping them apart.

Jonathan Brackley, Sam Vincent and David Wolstencroft wrote it, and Paul Whittington directed. Richard Armitage's Lucas carries the personal thread, with Peter Firth's Harry, Nicola Walker's Ruth Evershed and Shazad Latif's Tariq Masood around him. Sophia Myles joins as Beth Bailey and Max Brown as Dimitri Levendis, while Simon Russell Beale's Home Secretary, Iain Glen's Vaughan Edwards, Robert Glenister's Nicholas Blake and George Georgiou's Theo, the first mate, fill out the hour. Beth and Dimitri are new furniture, and the hour puts them in the room without fanfare.

A naval launch and a boatload of lethal cargo are a lot to stack, and adding a man from Lucas's past should break the balance. It does not. But the ghost is the reason to stay for the series, which is exactly the trick a season opener is for. There is a coldness to the opener that suits the mood, and it does not let up.