One of the few full-length novels by Sapper, in which the Bulldog Drummond does not appear. He does, however, show the second most important character, Ronald Standish. The two most intelligent characters were villains, but their schemes and plots remained mysterious for most of the novel. We are also told that all victims die from the same poison from a small scratch on the body, although the exact poison is nobody known. This is an unusual novel, which is full of mysteries.

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