A young inventor - the man whose name appears in the title of Dr. Watson's narrative, "The Adventure of the Bruce-Partington Plans" - lies dead on the floor of an old house, two bullet holes in his back. To solve the gruesome murder, Sherlock Holmes enlists the aid of William Gillette, the celebrated American actor renown for his portrayal of the famous detective, and Arthur Conan Doyle, conveniently familiar with the world of spiritualism that serves as backdrop to the brutal crime. In a plot replete with foreign spies, young lovers, eerie séances, and an array of the dead inventor's strange mechanical devices, Sherlock Holmes and Dr. Watson press on to discover the identity of Bruce-Partington's cold-blooded killer.