Death in a Downpour — Katherine McComb

Alf Trueblood and his fiancee, Karen Crandall, had come to Robber's Roost to rest and relax and go duck hunting, and thus cure Alf's nervous condition, the result of his Korean War experiences. Wind and storm and tales of buried treasure were not exactly calming, but they were as nothing compared to the deluge of murders which started corpses to falling faster than ducks.

The first victim was the landlady, the ineffable Mrs. Gaston. That left surviving as suspects, in addition to Karen and Alf, the victim's spinster sister; her simple-minded son; the maid, whose name was Myrtle Sparks but whose handkerchiefs were all embroidered with the initial B; and assortment of lodgers and even a possible non-registered guest.

A suspenseful baffler with a real surprise ending.