The year is 1898 and summer is just arriving in Karlshamn. Vicar Simon Eldfeldt has recently become a father for the first time and is filled with love for his newborn son. But his age, obesity and worry about his unruly nephew Ivar Jönsson is a constant burden on his mind.

Then two women are found dead, floating in the river that runs by the town, and soon more bodies are discovered. Fear and superstition starts spreading through the local population – could it be that Näcken, the evil water sprite, is behind the killings? Vicar Eldfeldt and Ivar Jönsson is once again faced with a complicated and possibly lethal investigation.