After our narrator Dr. John Watson gets married (to Mary Morstan, in Conan Doyle's second Sherlock Holmes novel, The Sign of Four) he doesn't see Holmes quite as often as he used to. As Watson sets up a happy home with his wife, Holmes remains as weird as ever, hanging around their old place in Baker Street and alternating between cocaine and criminal cases. Watson happens to be passing his former apartment on the walk back from his medical practice one evening, and decides to stop in to see his old pal Holmes. The two bat jokes back and forth about Holmes's deductive ability. Holmes finally comes out and asks if Watson can even recall the number of stairs that lead up to the 221B Baker Street apartment, and Watson admits that he cannot. "Ah ha " crows Holmes: proof that, while Watson sees the same things that Holmes does, he fails to observe them.