After the mysterious disappearance of her father the beautiful Miss Morstan starts to receive a present each year - a rare pearl. Who is sending the pearls and why does her secret benefactor suddenly want to meet with her?
The spellbinding mystery unfolds as Sherlock Holmes and his friend Dr. Watson are caught up in a cat-and-mouse chase pursuing an Indian treasure and a murderer whose ominous trademark is 'the Sign of Four'.