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. 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.