It is the end of the nineteenth century, and Sherlock Holmes, the world-famous detective, lives at 221B Baker Street in London. The great capital is a rainy, foggy city, where the police often have difficulty in catching criminals. Luckily, Holmes is there to help them, but only if a case is interesting enough.

Holmes is extremely intelligent, and intelligent people are often impatient with their friends. 'Think, Watson!' he says sharply to the good doctor, who is not as clever or as quick as he is. But he sometimes needs Dr Watson's help, and is grateful for it, especially in a dangerous situation.