“The Sign of Four” was first published as a book in 1890.
Arthur Conan Doyle’s second Sherlock Holmes novel first appeared in the February 1890 issue of Lippincott’s Monthly Magazine, under the longer title “The Sign of the Four; or The Problem of the Sholtos.” Spencer Blackett then published it in book form in October 1890, using the shorter title “The Sign of Four.”
This distinction matters because the magazine appearance and the book publication happened in the same year but were separate stages. Some references therefore describe the work simply as an 1890 novel, while others emphasize its February serial debut or October book edition.
The story introduces Mary Morstan, the Agra treasure, and the sign formed by the four conspirators. It was not initially a major commercial success. Doyle’s Sherlock Holmes short stories, beginning in The Strand Magazine in 1891, soon made the detective and his creator internationally famous.