This is the 7th Ellery Queen novel, THE SIAMESE TWIN MYSTERY. Another sentimental favorite of mine, it’s the first of the early books that I was able to local in a middle school library, of all places. (The library book was a hardcover Gollancz edition.) The plot is a twist on the old British trope of the isolated country house. Here, the denizens of the country house, including Ellery and his father, are cut off from humanity by a raging forest fire. There really is a set of conjoined twins, and a creepy dying clue: a playing card depicting the Jack, torn in half.
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