Dr. Watson is called to 221b Baker Street to check on Holmes, who is apparently dying of a rare Asian disease contracted while he was on a case. Watson is shocked, having heard nothing about his friend’s illness. Mrs. Hudson says that he has neither eaten nor drunk anything in three days. Upon arriving, Watson finds Holmes in his bed looking very ill and gaunt indeed, and Holmes proceeds to make several odd demands of Watson. He is not to come near Holmes, for the illness is highly contagious. He will seek no help save from the man whom Holmes names. He will wait until six o’clock before Holmes names him. When Watson objects and tries to leave for help, Holmes musters enough strength to leap out of bed, and lock the door, taking the key. So, Watson is forced to wait. Holmes seems delirious at times.
Watson examines several objects in Holmes’s room while he waits. Holmes has a fit when Watson touches one item, a little black and white ivory box with a sliding lid. Holmes orders him to put it down, explaining that he does not like his things touched.
At six o’clock, Holmes tells Watson to turn the gaslight on, but only half-full. He then tells him to fetch Mr. Culverton Smith of 13 Lower Burke Street. Oddly, he also tells Watson to be sure that he and Smith return to Baker Street separately. Smith is not a doctor but is supposedly an expert on the illness that ails Holmes. Also, Holmes explains that Smith does not particularly like him, for Holmes once cast the suspicion for Smith's nephew’s murder on him…
(Excerpt from Wikipedia)