For Miss Cordell, principal of Persephone College, there are two great evils to be feared: unladylike behaviour among her students, and bad publicity for the college. So her prim and cosy world is turned upside down when a secret society of undergraduates meets by the river on a gloomy January afternoon, only to find the drowned body of the college bursar floating in her canoe. The police assume that a student prank got out of hand, but the resourceful Persephone girls suspect foul play, and take the investigation into their own hands.