The Red-Headed League by Arthur Conan Doyle

A red-haired man is hired for an unusual job that involves copying out an encyclopedia—but Sherlock Holmes soon suspects a criminal plot behind the seemingly harmless task. With Watson at his side, Holmes uncovers a cunning plan involving tunnels, deception, and a planned robbery. The plot is concise and cleverly structured, leading to a satisfying resolution. This case highlights Holmes's deductive brilliance and attention to detail. It's one of the most popular and ingenious of his short adventures.