As a dense yellow fog swirls through the streets of London, a deep melancholy has descended on Sherlock Holmes, who sits in a cocaine-induced haze at 221B Baker Street. His mood is only lifted by a visit from a beautiful but distressed young woman - Mary Morstan, whose father vanished ten years before. Four years later she began to receive an exquisite gift every year: a large, lustrous pearl. Now she has had an intriguing invitation to meet her unknown benefactor. In a letter, he promises to reveal the mystery and to ''right the wrongs'' against her. ''If you distrust me,'' he wrote, ''bring two friends.'' She brings Holmes and Watson, and in the ensuing investigation - which involves a wronged woman, a stolen hoard of Indian treasure, a wooden-legged ruffian, a helpful dog and a love affair - even the jaded Holmes is moved to exclaim, 'Isn't it gorgeous'.