The Sign of the Four

The Sign of the Four, published in 1890, is the second Sherlock Holmes novel by Sir Arthur Conan Doyle.

The story begins with Miss Mary Morstan seeking Holmes' help regarding a series of mysterious pearls she has received.

The investigation leads to a complex plot involving service in India, the Indian Rebellion of 1857, a stolen treasure, and a secret pact among four convicts and two corrupt prison guards.

The novel explores themes of betrayal, revenge, love, and justice, while showcasing Holmes's remarkable sleuthing abilities.

It also introduces Doctor Watson's future wife, Mary Morstan, and humanizes Holmes by revealing his drug habit and personal struggles.