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.

A female bishop visiting St Gerard's College is found dead after drinking poisoned wine, and when another two killings occur, both mirroring macabre murders from Jacobean revenge tragedy, it appears the culprit is targeting candidates in the election to become vice-regent. However, when Innocent learns one of the suspects is hiding a dark secret, Lewis and Hathaway realise the motive is much more twisted.

When a student is found dead during a college-based clinical trial for a new anti-depressant, Lewis and Hathaway struggle to determine whether the incident was murder or suicide, and receive little assistance from the institution's evasive psychiatric professor. A second student's death then leads to the revelation that the trial's participants are all operating under the influence of mind-altering drug ketamine, and that the lines between love, obsession and madness have become dangerously blurred.

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.