Book 8 in The Police Doctor Investigates series 

A doctor does some sleuthing of her own when, following a murder, the police fish with rotten bait…
With the fishing industry on its knees, it doesn’t come as a huge surprise to find a boat owner hanging by their neck.
But when the unfortunate man’s father is also found dead by the same means, police doctor Callie Hughes smells something fishy.
She is not convinced it is suicide, and manages to persuade her partner, Detective Inspector Steve iller, to treat it as murder.
But he has an obvious suspect in mind, one who is evading the authorities, and puts aside Callie’s concerns to focus on catching him.