"A great brain in London and a dead man in Sussex. It's the chain between that we are going to trace." The famous detective Sherlock Holmes has been summoned by a coded message to the house of a man called Douglas. But he and his faithful associate Dr. Watson arrive to find they are too late: Douglas has been murdered, with a mysterious calling card left by his side. Scotland Yard is stumped, but Holmes, detecting the diabolical workings of his arch-enemy Professor James Moriarty, has some ideas of his own.