The Valley of Fear
The series has 64 episodes, including the multi-part adaptations of the novels "The Hound of the Baskervilles" (3 episodes), "The Valley of Fear" (2 episodes), and "The Sign of Four" (3 episodes). A double-length episode, "The Return of Sherlock Holmes", combines Doyle's short stories "The Final Problem" and "The Adventure of the Empty House". The episodes based on "A Study in Scarlet" and "The Adventure of the Speckled Band" are also double-length, as are the episodes adapted from "The Hound of the Baskervilles" and "The Valley of Fear".