This used to be my favorite among Ellery Queen's early books, and I remembered much of its menace and grotesquerie fondly, but taking it off the shelf again I spoiled it for myself. As a child I gaped to read about John Xavier, the "mad scientist" with cages full of animals, in pairs, like some mad Noah without the Ark, a scientist who built himself a country house, "Arrow Head," at the top of the Tepee Mountains up New England way. The story has atmosphere, atmosphere enough for a better plot than the one they've given us. How many Ellery Queen books have the same storyline where first the police and Ellery arrest one suspect, based on "airtight" deductions on EQ's part, then they find out, oh, they were wrong, and arrest another clown, and then, once again, oh I'm sorry, you were innocent too? (I just finished THE FOURTH SIDE OF THE TRIANGLE where this plot is even more absurdly worked up.)
But in general, THE SIAMESE TWIN MYSTERY may be the best novel I've ever read about a forest fire, as the mountain blazes up and Ellery & company are trapped in the mansion at the very top of the impossibly twisty mountain road--trapped for days while their situation grows increasingly worse. By the end of the book you wonder, how the devil are they ever going to get out to this nightmare?
Who killed John Xavier and why is he clutching half of a playing card--the six of spades--in his vivisectionist hand? Another victim croaks and his last word is "I." Crazy me suspected until long after the book was over, that the killer would turn out to have one of those names, like "Eileen," in which the first syllable would sound like "I." After Ellery's complicated reasoning in the matter of the "Six of Spades" clue, you will agree that I'm hardly out of line pursuing this ludicrous possibility. It would have made a great 30s movie, with Charles Laughton as Xavier, Judith Anderson as his wife, Dolores del Rio as Marie Carreau, Freddie Bartholomew (and himself) as the twins, Alice Faye as Ann Forrest the comely companion, and perhaps lean, saturnine Raymond Massey as Mark Xavier, the doctor's shady brother. Oh, and Sydney Greenstreet as the threateningly fat lump, "Smith." (Didn't you think "Smith" was going to turn out to be the first husband of Sarah Xavier? Whatever happened with that line of questioning? It seems Ellery and his dad, Inspector Richard Queen of the NYPD, just accept Mrs. Xavier's assurances that her first husband was not a factor in this crime. Well, check, boys!)