The Cottage With Too Many Keys — Robert W. Gregg

Summer residents return to Crooked Lake after a long, cold winter and are horrified to find the body of a beautiful young woman in the cellar of their cottage. The sheriff identifies her as an exchange student from Sweden who went missing back in January. But how did her body come to be in a cottage which had been closed and locked up since the previous September? The sheriff and her partner soon find themselves in search of the person who had both a reason to kill the young woman and a key which provided access to the cottage.