Over an August Bank Holiday, an empty Oxford college is the venue for a weekend attended by professional quiz contestants. Lewis and Hathaway are called in when outstanding competitor Ethan Croft is found floating dead in the college fountain. They learn that Croft was an outrageous flirt with a number of secrets, and the pair race to uncover the killer before the gathering breaks up. Meanwhile, Hathaway discovers that Lewis was planning a romantic weekend at Glyndebourne with a mystery date.