Cambridge, 1898. When the unidentified body of a young woman is found floating in the River Cam, journalist Patrick O'Sullivan calls on the one woman he is sure will solve the mystery: Mrs Vanessa Weatherburn. Vanessa agrees to takes up the challenge, but, with a victim as well as a murderer to identify, she knows it will be no easy task. Forced to go undercover while investigating the owners of Heffer's bookshop, and helped along by the cream of Cambridge's academic community, Vanessa employs all her skills to reel in the killer - but will it be enough to solve the riddle of the river?