The Sign of Four.

The Sign of Four is the second Sherlock Holmes novel and one of Arthur Conan Doyle’s most energetic full-length mysteries. A visit from Mary Morstan leads Holmes and Watson into a case involving a vanished treasure, cryptic annual gifts, a locked-room death, and a chain of secrets reaching from Victorian London to the aftermath of British imperial rule in India.

Themes

The novel combines brisk detective plotting with questions of loyalty, greed, colonial violence, and the limits of official respectability. Holmes’s methodical intelligence is matched by Watson’s emotional and moral perspective, making the case both a puzzle and a character study.

Why readers still return to it

The Sign of Four remains one of the most satisfying Holmes adventures because it balances deduction, atmosphere, chase narrative, and memorable supporting characters while sharpening the Holmes–Watson partnership.

Further context

Published in 1890, the novel helped establish Sherlock Holmes as a durable global detective figure and remains central to the early Holmes canon.