"The Adventure of the Dying Detective" by Arthur Conan Doyle is a short story published in 1913. Dr. Watson rushes to Baker Street after learning that Sherlock Holmes is apparently dying from a rare tropical disease. The detective refuses Watson's medical help and behaves strangely, insisting instead on a visit from Culverton Smith, a man connected to a suspicious death. As Watson watches events unfold, he discovers that nothing is quite as it seems in this tale of deception and murder.
Wikipedia page about this book: en.wikipedia.org/wiki/The_Adventure_of_the_Dying_Detective