Salmander goes undercover in Solvik jail to follow a lead in the murder case. When his only ally in prison dies from a peanut-related accident, Salmander is put behind bars for real. Not only must he follow a trail in the case, he must also find a way to get out of prison. Meanwhile, Johanne finds a very special clue in Hellfjord's murder mystery.

Salmander and Johanne sneak into Hellfish at night and come across something strange. They overhear Bosse Nova talking about the infamous serpent Tulla, and despite Salmander's chronic seasickness he decides to defy his fear and look into this phenomenon.