The challenge is to read (or re-read) all Sherlock Holmes books:
1. A Study in Scarlet (1887)
2. The sign of the Four (1890)
3. The Adventures of Sherlock Holmes (1892)
4. The Memoirs of Sherlock Holmes (1894)
5. The Hound of the Baskervilles (1901-2)
6. The Return of Sherlock Holmes (1905)
7. The Valley of Fear (1914-15)
8. His Last Bow (1917)
9. The Case-Book of Sherlock Holmes (1927)