Gray Norris visits his friend Keeley Moore, a private detective, at his summer house by the lake. Not long after, neighbor Sampson Tracy is found dead in his bed, a nail driven in his skull, wrapped in flowers and a lady’s silk scarf, with a feather duster propped up behind his head, and his watch at the bottom of a water jug. Stolen from the room were two satin waistcoats and a souvenir totem pole. The door was locked, of course, and the windows opened out to the Sunless Sea — a part of the lake with especially treacherous rocks and currents.
Tracy was about to marry Katharine Dallas, although it’s not so much a secret that she wanted him for his money. She’s in love with Charles Everett, Tracy’s secretary. But with the wedding not yet performed, Tracy’s estate stands to go to his niece, Alma Remsen, his only living relative since the death of her twin sister Alda, besides substantial bequeaths to his servants and his closest friend, Harper Ames. Ames, it seems, was heavily in debt to Tracy at the time of his death. Alma previously lived with Tracy until the advent of Dallas, when she moved to a solitary island, living in near seclusion with her two trusted servants, although the guest room does seem strangely lived in. Dallas, Tracy, and Alma argued the last time they spoke, with Tracy wanting to tell Dallas a secret, Alma not wanting him to, and Dallas refusing to hear it.
Keeley Moore sees only one way the murderer could have escaped, and that’s through the window and into the Sunless Sea. We’re looking, then, for an expert diver and a strong swimmer thoroughly familiar with the cove’s hidden dangers, much like Alma Remsen. Indeed, her fingerprints are on the window sill and the waistcoats and totem pole are found in her boathouse. That the murder chose such violent methods and then so strangely decorated the corpse suggests a form of madness, maybe dementia praecox (what we’d call schizophrenia today). Doctor Rogers, who cared for all the Remsens, is away in San Francisco, but wires that there is dementia praecox in the family. Everyone seems convinced by the evidence, except Gray Norris, for the simple fact that he’s fallen in love with Alma and can’t see her as a homicidal maniac, even though he’s concealing the fact that he witnessed her rowing away from the Tracy house in the dark of night just after the murder.
Gray is right, of course. Did you pick up on the oh so subtle clues? A Remsen is afflicted with dementia praecox, but it isn’t Alma — it’s her sister Alda, who is not dead. When the girls both contracted scarlet fever, Alma was left partially deaf while the mental changes in Alda were profound. It was pretended that Alda died so that she could be kept hidden and give her the most pleasant life possible. Her world has been disturbed by moving to the island and she’s grown violent. That was Tracy’s secret. Because he was so adamant to tell Dallas about Alda, Alda murdered him. It was her fingerprints on the window and her that Gray saw rowing away — Alma and Alda are identical twins.
Inscriptions. Signed John Naum on the front flyleaf.