Crucially, Watson observes that Amberley is painting a door and passageway in his house with a strong-smelling green paint. Watson also notices a tall, dark, mustached man who follows him when he leaves Amberley’s house. This is enough to engage Holmes’s suspicions. Holmes despatches Watson and Amberley on a wild-goose chase to Essex using a false telegram purporting to come from a vicar named Elman. With them out of the way, he establishes that Amberley’s alibi for the night of his wife’s disappearance (a theater trip) is false. Holmes then breaks into Amberley’s house and discovers, behind the freshly painted door, a sealed chamber with a telltale gas inlet pipe—a perfect murder room. Amberley lured his wife and her suspected lover into the chamber and trapped them there, flooding the room with poisonous gas.

The mysterious dark man spotted by Watson turns out to be Holmes’s rival, the private investigator Mr. Barker, who has been hired by Dr. Ernest’s family. Unusually, the two join forces, handing over the murderer to Inspector MacKinnon of Scotland Yard. Holmes instructs the inspector to look for conclusive evidence of the murder around the house, including in a disused well, and the bodies are duly discovered. The inspector shows his genuine respect for Holmes when he states, with admirable understatement, that “it’s as workmanlike a job as I can remember.”

Amberley’s approach to the authorities, and latterly Holmes, was “Pure swank”—the murderer had complete confidence that he would not be outwitted by either the police or the renowned detective.

Holmes observes that Amberley’s mind was deranged by jealousy, and it is probably no coincidence that Amberley used green paint (the color associated with jealousy) to mask the smell of gas emanating from the murder chamber. Holmes sees the extreme cruelty of the murder as a sure sign of madness, and suggests that Amberley is more likely to end up in the Broadmoor asylum than on the gallows.

This story is lighter and more playful in tone than the melancholy of the opening would have the reader believe. Assigning Watson an investigative role inevitably leads to some witty banter between the two friends, as they contrast their abilities. Holmes is depicted at his enterprising best as a hyper-observant cat burglar, and the police are, as usual, left flat-footed. Although Holmes has solved the crime, he does not seek public recognition, and seemingly enjoys reading accounts of the case that credit the police with solving the mystery. However, he still suggests, in his wry way, that Watson make a record of the events, saying, “Some day the true story may be told.”