Episode 5

AC-12 links Gail Vella's murder to a historic case of police corruption, and the investigation suddenly has a shape. Kate hatches a plan to find out once and for all whether Jo is bent, and the test is set in motion. They are closer than ever to cracking the case. Then Hastings's authority is undermined, and the team is left in a potentially dangerous position. The historic case is the one the force thought was closed, and it was not.

The episode is about the moment when an investigation becomes a gamble. Kate's plan for Jo is a high-stakes test, and the result will change everything either way. The link to a historic case of corruption gives the story depth, and the show handles the connection with its usual patience. But the attack on Hastings's authority is the other shoe dropping, and it leaves the unit exposed at the worst possible time. The ground is shifting under everyone, and nobody has a firm footing. The episode has the feel of a machine being wound up, and the winding is audible.

Jed Mercurio wrote it, Jennie Darnell directed. Vicky McClure's Kate takes the risks this week, and Kelly Macdonald's Jo keeps the audience guessing to the last. Martin Compston's Arnott, Adrian Dunbar's Hastings, Shalom Brune-Franklin's Bishop, Perry Fitzpatrick's Lomax, Gregory Piper's Pilkington, Owen Teale's Osborne, Ace Bhatti's Sindwhani and Amy De Bhrún's Corbett complete the cast. It is a strong company, and the episode trusts it with a week of difficult scenes.

The episode is about how quickly the ground can shift under an investigation. The historic corruption case is the key to everything, and the team is finally holding it. Whether they can hold it long enough is the question the episode leaves hanging. But the test of Jo is coming, and the result will not be comfortable for anyone. Hastings's fall, if it comes, will take the team down with him, and the episode makes that plain. The plan is set, the test is prepared, and the countdown has started.