Oxford's last all-female college is holding a reunion party to say goodbye to one of its most popular professors. After a guest is found murdered, Lewis believes the killing is connected to an attack that happened at the same building 10 years ago. He turns to his former DS, Alison McLennan, to help him with the case, but it ends up taking a new twist after two more bodies turn up.

The ethics of a questionable drug on the Oxford campus of anti-depressants calls into account the questionable judgment of a psychiatry professor.

When a local businesswoman is bludgeoned to death, it appears to be a blackmail plot gone wrong. As the body count rises, Lewis and Hathaway realize there is a decades-old secret at the heart of the case, which they must uncover to bring the present-day murders to a halt.