รายละเอียด(อย่างย่อ) 'He's an intelligent man. He was once rich and is now poor. His wife loved him once, but she doesn't love him now. And he's thirty or forty years old.' One look at an old hat, and Sherlock Holmes can tell you a lot about its owner. He sees - and thinks - a lot more than the people around him, and when a beautiful blue diamond disappears, Sherlock is the only man in London who can find it.