The Sign of the Four (1890), also called The Sign of Four, is the second novel featuring Sherlock Holmes written by Sir Arthur Conan Doyle.

Doyle wrote four novels and 56 short stories featuring the fictional detective.
(from wikipedia.org)

Sir Arthur Ignatius Conan Doyle (1859 - 1930) was a British writer best known for his detective fiction featuring the character Sherlock Holmes.

Originally a physician, in 1887 he published A Study in Scarlet, the first of four novels about Holmes and Dr. Watson.

In addition, Doyle wrote over fifty short stories featuring the famous detective.

The Sherlock Holmes stories are generally considered milestones in the field of crime fiction.
(from wikipedia.org)