Set in 1888, the story revolves around the case of Miss Mary Sutherland, a woman with a substantial income from the interest on a fund set up for her. She is engaged to a quiet Londoner who has recently disappeared. Sherlock Holmes's detective powers are barely challenged as this turns out to be quite an elementary case for him, much as it puzzles Watson.
The fiancé, Mr. Hosmer Angel, is a peculiar character, rather quiet, and rather secretive about his life. Miss Sutherland only knows that he works in an office in Leadenhall Street, but nothing more specific than that. All his letters to her are typewritten, even the signature, and he insists that she write back to him through the local Post Office.
The climax of the sad liaison comes when Mr. Angel abandons Miss Sutherland at the altar on their wedding day.
Holmes, noting all these things, Hosmer Angel's description, and the fact that he only seems to meet with Miss Sutherland while her disapproving youngish stepfather, James Windibank, is out of the country on business, reaches a conclusion quite quickly. A typewritten letter confirms his belief beyond doubt. Only one person could have gained by this: Mr. James Windibank. Holmes deduces "Angel" had "disappeared" by simply going out the other side of a hansom cab.
After solving the mystery, Holmes chooses not to tell his client the solution, since "she would not believe me... There is danger to him who snatches a delusion from a woman." In this, however, he can be accused of not fulfilling his professional duty for which he was paid - namely, to investigate the matter to which she set him, provide her with the results and let her decide what to do with them. Holmes does advise his client to forget "Mr. Angel"; Miss Sutherland refuses to take Holmes advice and vows to remain faithful to "Angel" until he reappears-for at least 10 years.
One may wonder whether Dr. Watson disagreed with Holmes' behaviour in this matter, since he published an account of the whole story a few years later. Holmes' conclusions would then surely find their way to Miss Sutherland as well, though she would hardly be glad to find that the whole story had been turned into entertainment for the masses. Watson's description of herself, including references to her "preposterous hat" and "vacuous face", would probably not be much appreciated either.
Holmes predicts Windibank will continue a career in crime and end up on the gallows.
Several other Sherlockian tales involve disguise for deceit.