The Adventure of the Engineer's Thumb

A young hydraulic engineer named Victor Hatherley is brought to Dr. Watson's office after losing his thumb in a gruesome accident. He tells a bizarre story: he was hired by a mysterious man, Colonel Lysander Stark, to inspect a hydraulic press at a remote country house — at night and for a very high fee. During the inspection, Hatherley discovers that the press is being used to counterfeit coins. When he tries to leave, he is attacked. He escapes but loses his thumb to a cleaver-wielding attacker. Holmes realizes that the "Colonel" is a clever criminal and rushes to the house, but the criminals have already fled, setting the house on fire. Though Hatherley loses his thumb permanently, he escapes with his life. Holmes observes that the case is less about justice and more about the strange opportunities that exist in criminal London.