Summary
Peterson, a commissioner, brings to Holmes a hat that was left by a man, along with a Christmas goose, who ran away when Peterson rushed over to try to save him from a fight. Holmes at first tries to deduce for whom the goose was intended, but Peterson returns with the discovery in the goose's crop of a famous jewel, the blue carbuncle owned by the Countess of Morcar, which was recently reported as stolen. John Horner, a plumber who was at the Hotel Cosmopolitan, the hotel where the Countess was staying at the time of the theft, was accused of the crime, but Holmes suspects someone else.
Holmes traces the path of the goose back to its source, beginning with the Alpha Inn, where it was sold. He then goes to Mr. Breckinridge, a salesman, from whom he learns the goose came from Mrs. Oakshott. Visiting Mrs. Oakshott, Holmes comes across James Ryder, the head attendant at the Hotel Cosmopolitan, who stole the carbuncle after hearing of it from Catherine Cusack, the Countess' maid. After the theft, Ryder had struggled for an idea to conceal the carbuncle, lest it were found it his person; but his idea of stuffing it down a goose's crop backfired when he lost track of the goose.
Holmes lets the man go.
Analysis
This story takes a peculiar structure whereby Holmes' usual deductive fireworks from observing an object, in this case Henry Baker's hat, reveals detailed information that has a completely different relevance from what he thought it would have. Once Peterson shows up with the carbuncle, Holmes realizes that what he had taken for a case of simple fun is in fact of a much greater importance, and that finding Henry Baker is just the first step in a longer chain of identities to discover. This gives the reader the sense that the seemingly insignificant but highly curious mysteries that attract Holmes attention sharpen his skills for cases of importance.
The conclusion of the tale, with Holmes' usual confrontation with the criminal, takes an unusual turn in that Holmes practically pardons the man.
Holmes' explanation of why he has let Ryder off the hook reveals much about Holmes' ethos as an investigator and moral man: "I am not retained by the police to supply their deficiencies. If Horner were in danger it would be another thing; but this fellow will not appear against him, and the case must collapse. I suppose that I am commuting a fellow, but it is just possible that I am saving a soul. This fellow will not go wrong again; he is too terribly frightened" (175).
