Señal de los Cuatro

Señal de los Cuatro, written by Sir Arthur Conan Doyle in 1890, is a detective novel featuring Sherlock Holmes and Dr. Watson. The story begins when a woman seeks Holmes's help to visit a man, leading to the revelation of a secret surrounding a treasure discovered in India. This novel is notable for introducing the character of Mary Morstan and for its exploration of themes such as loyalty and betrayal.