1898. Enjoying the sunshine in her Cambridgeshire garden, Vanessa Weatherburn is startled by the abrupt arrival of her friend Patrick O'Sullivan. Eager to discover the identity of a young woman found floating in the River Cam to get a scoop for the local newspaper, he is sure Vanessa can solve the mystery. After attending a seance in London she is forced to go undercover to continue her investigation, and helped as always by the cream of Cambridge's academic community, Vanessa employs all her skills to reel in a murderer - but will it be enough to solve the riddle of the river?