London, October 1968. As Beatles fans encamp outside Abbey Road Studios up the road, the Marylebone CID is as much an old boys' club as it ever was: comfortably sexist, racially prejudiced and crawling with corruption.
Detective Sergeant Cathal Breen is the pariah of the office, having just run out on a fellow officer held at knifepoint, when it's shaken up by the arrival of WPC Helen Tozer: awkward chatterbox, farmgirl, and the first woman to enter the murder unit - apart from the secretary.
When a young woman is found naked and strangled in well-to-do St John's Wood, her identity is a mystery. The neighbours offer nothing but xenophobic suspicions, witnesses are staying silent; only Tozer's savvy gives Breen a lead.
Following it, resourceless, deep into the rural backwaters, Breen sees one dead body lead to another - a trail of bloodshed taking them dangerously close to a killer with everything to lose...