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 and urges Holmes and Watson to accompany her. 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!'