"The Adventure of the Devil's Foot" by Arthur Conan Doyle is a short story written in 1910. While vacationing in Cornwall, Sherlock Holmes and Dr. Watson are drawn into a baffling case when three siblings are found in their home—two driven mad and one dead. When a fourth family member dies similarly, Holmes discovers a deadly poison that attacks the mind. The investigation reveals a tale of forbidden love, revenge, and a lethal substance from Africa called Devil's-foot root, forcing Holmes to weigh justice against morality.