Loyalty can be a one-way street, as evidenced in this episode in which both Maeve and Conrad Harrigan immediately suspect Harry of being a rat, the worst possible sin in their crime family universe, after the coppers find Archie's corpse. The audience knows Harry is 100% loyal to the Harrigans, a fact underscored by a scene of his wife saying as much to her therapist, but it is telling how easily they can turn against their most loyal employee.
This episode delves into the psychology of the characters more than previous ones, especially Harry's world view versus that of such a "normal" character as his wife Jan (well-played by Joanne Froggatt). I was especially grateful to have her, one of the story's "civilians", get a bit of spotlight in a series otherwise dominated by, in every sense, the repellent criminals.
A major script failing here is the weak set-up of how easily and quickly our stars Pierce and Helen turn against Harry - I didn't buy it, but writers Bennett and Butterworth assume the audience will accept such crucial plot twists without batting an eyelash. The whole series not merely revolves around Harry but is based on viewer identification with him, so such a drastic switcheroo requires a lot more convincing evidence.
To keep the pot boiling, there's plenty of treachery afoot with way too much giving away of devious motivations (especially Maeve's) for my taste. In the final analysis, the question of viewer loyalty to a fledgling TV series (we're only in the fourth installment) is paramount, pun intended.
