The Things We Do for Love

Vicky Philips, a local physiotherapist, is found brutally stabbed in a car park, and the case lands Frost with a new partner: DS Frank Nash, recently married, already fraying under the strain of a job that never lets him go home. The investigation circles the respectable surface of Denton's religious community before finding the rot underneath.

Vicky had been due to see Jonathan Meyerbridge, a leading figure in the local church with a past arrest for assault, and love letters between them reveal the affair she was having with him — secret rendezvous in an apartment above a butcher's shop run by Sykes, one of Meyerbridge's followers. Meyerbridge's defence is orchestrated by Edward Gull, a solicitor with a seat on the board that oversees police affairs, who has coached the suspects through interrogation and, Frost suspects, may be in love with Meyerbridge himself. The case is sliding away until forensics enhance the recording of the call that reported the murder: in the background, a radio that belongs to Milly, the Meyerbridges' live-in nanny.

Milly confesses. A young woman with a troubled past — crime, abandonment, a life spent on the edges — she killed Vicky because Meyerbridge was planning to leave his wife for her. She wanted to stop him destroying his family. The murder, in other words, was an act of devotion, and the episode's title is the knife twisting: everything these people do to each other, they do out of love.

Underneath, the episode tracks Nash's collapse. He tells Frost he means to resign to save his marriage, and Frost, who has never managed to save his own, tells him that he has the makings of a fine officer — a benediction from the series' most broken relationship to its most hopeful one. The Things We Do for Love, written by Alma Cullen and directed by Adrian Shergold, is anchored by Michael Kitchen's Meyerbridge, all sanctimony and appetite, and by Sara Stephens' Milly, whose confession is the episode's most human moment.

The title is the knife: every death in this episode is an act of love, and the series has never been so bleak about what people will do for it. A bleak study of devotion and the damage it leaves behind.