Three of the Sherlock Holmes novels

Sir Arthur Conan Doyle wrote only 4 crime novels featuring the Detective Sherlock Holmes.

The first three of them are:

• A Study in Scarlet (published 1887, in Beeton’s Christmas Annual)
• The Sign of the Four (published 1890, Lippincott’s Monthly Magazine)

• The Hound of the Baskervilles (serialised 1901–1902 in The Strand)

Which is the last one?

Images: Wikipedia