Mary Morstan, a lovely young woman, comes to the Baker Street lodgings shared by Holmes and Dr Watson. Her mother died when she was very little and her father, an army Captain stationed in India, sent the child back to England to live in a boarding house. She had never seen her father, but ten years earlier, when she was seventeen she received a letter from him saying he had retired, was on his way home and asking her to meet him at the Langham Hotel in London. However, at the Langham, she discovers that her father stepped out the previous evening and never returned. Since then, every year, on her birthday she has been receiving a present from an anonymous giver. It is a very expensive, lustrous, single pearl. And now, she has received a mysterious letter asking her to come to the Lyceum Theater at seven in the evening, bringing two friends with her. For Sherlock Holmes, this is an enigma that's simply crying out to be solved!

Added to this are masterly touches that provide more insights into Holmes' unconventional persona. His uncanny ways of tracking through sight, sound and smell, his knowledge of diverse subjects and his fondness for obscure quotations in foreign languages are all aspects that went into the creation of the immortal detective.

Following the publication of The Sign of the Four, Doyle began concentrating on the short story format featuring Holmes and Watson. This met with immediate success and led to a revived interest in the novels and the rest, as they say, became literary history.

The Sign of the Four has been adapted extensively on stage, screen, TV and radio. In fact, more than eighteen different film versions have been made since 1913-2013, marking a century of perennial interest in the maverick sleuth and his faithful assistant!