The Siamese Twin Mystery (1933)

The Siamese Twin Mystery (subtitled A Problem in Deduction) is an English language American novel written in 1933 by Ellery Queen. It is the seventh of the Ellery Queen mysteries.

Plot summary

Inspector Queen and his son Ellery are vacationing in a mountainous area of the United States when they are forced by a forest fire to seek shelter at Arrow Head, the mountaintop home of famous surgeon Dr. John Xavier, which soon becomes impossible to escape due to the fire. There the sleuths meet an unusual assortment of characters, beginning with Dr. Xavier and his wife Sarah; his brother Mark; his medical assistant Percival Holmes; his handyman "Bones"; the housekeeper, Mrs. Wheary; and a houseguest, Ann Forrest. Miss Forrest has recently lost a silver ring; Dr. Holmes likewise finds himself missing a cheap signet ring. That night, Ellery spies a strange crab-like shape moving in the upstairs hallway, and, independently, Inspector Queen discovers that also present at the house is the wealthy Marie Carreau, a fixture of Washington high society; Ann is Mrs. Carreau's personal secretary. In the morning, Dr. Xavier is found dead in his study — shot twice with a revolver which has been wiped clean of any fingerprints. In his right hand he clutches the torn half of a playing card: the six of spades.

The previous night, the Queens had encountered on the road a heavyset and unsavory man, who — his escape blocked by the fire — now returns to the house, giving his name unconvincingly as "Smith." It is further revealed that Marie Carreau had come to the house to consult with Dr. Xavier on the subject of her teenage sons, Julian and Francis, who are xiphopagous conjoined twins. It was the twins who had cast the crab-like shadow seen by Ellery in the hallway. Meanwhile, the Inspector makes the connection between the six of spades and Mrs. Xavier's initials — Sarah Isère Xavier — and accuses her of murdering the surgeon in a jealous rage at his lengthy conferences with Mrs. Carreau. Mrs. Xavier instantly confesses to the murder and collapses in a faint. However, Ellery observes that Dr. Xavier, who was right-handed, would naturally have used his right hand to crumple and discard half of the card, which would leave the uncrumpled half clutched in his left hand. It follows that the playing card must have been torn and placed in Xavier's hand by some left-handed person — that is, by the murderer.

The Queens investigate Dr. Xavier's laboratory and find that Xavier has been experimenting with the separation of conjoined twins of various animal species — always without success — and that "Bones" has been burying the failures in the garden. That night, the Queens search Mrs. Xavier's jewel-box and find that it contains no rings at all. The next morning, the party attempt to find a way past the increasingly menacing forest fire, but to no avail. Ellery observes a conversation between Smith and Mrs. Carreau, and deduces that Smith had been blackmailing Carreau, threatening to publicize the existence of her sons — but that the murder, sure to draw publicity, had neutralized Smith's hold over Carreau. The Queens conduct a series of "tests" to prove that each member of the party is right-handed, except for Mark Xavier; on this evidence, Ellery accuses Mark of murdering Dr. Xavier and planting the card to throw suspicion on Mrs. Xavier. Mark, in a panic, tries to escape; Inspector Queen shoots him and returns him to the house, gravely wounded. Mark confesses that he planted the torn card to frame Mrs. Xavier, but insists that Dr. Xavier was dead before Mark entered the room — and insists that he knows who the killer is! But Holmes' morphine takes effect before Mark can reveal the murderer's identity. Inspector Queen stands watch over Mark and is there at 1 a.m. when Mark regains consciousness; but when Ellery comes down at 2 a.m. to check on his father, he finds the Inspector chloroformed and Mark Xavier dead — poisoned by oxalic acid — clutching in his right hand the torn half of a jack of diamonds.

Ellery finds Mrs. Carreau awake in her room, which is suspicious. Inspector Queen discovers that while he was chloroformed, somebody stole the wedding ring off his finger. The party return to their rooms. When somebody tries to break into the safe where Xavier's original deck of playing cards was being kept as evidence, Ellery on a hunch counts the cards in that deck and discovers that it is missing two cards — the six of spades and the jack of diamonds! The Queens deduce that when Mark found his brother's body, Dr. Xavier had been clutching a torn jack, which Mark replaced with the six of spades to frame his sister-in-law (because with her out of the way, Mark stood to inherit Xavier's estate). When Mark in turn was murdered, he must have decided that the best way to clue at his murderer's identity would be to reproduce Dr. Xavier's authentic clue — the jack of diamonds. Further, Ellery observes that the French name for the suit of diamonds is carreaux, and the image on a jack is that of two conjoined young men! He concludes that (because the card was torn in half) only one of the Carreau twins is the murderer, and suggests that the twin may have killed Xavier in self-defense, out of fear that Xavier would try (and fail) to separate the twins surgically. The Queens speculate on the "beautiful headache" such a case would present: Murder is a capital offense, but supposing only one of the twins to be guilty of murder, what would become of the other?