Maigret had been sent in disgrace from Paris to a backwater fishing community for an unexplained infraction (published in 1942 during the Nazi occupation of France, perhaps this was Simenon's way of avoiding Wehrmacht entanglements for his hero and himself?)
Maigret's boredom is alleviated by a tipoff from the local busybody about a corpse she's seen through her neighbour's back window. It's not just the fish that stinks in this excellent mystery!