"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. (This is an automatically generated summary.)
These books are free to read. Each is in the public domain in the United States; check your own country's rules before you copy or share one.