Dr. Watson is called to tend Holmes, who is apparently dying of a rare tropical disease, Tarpaunli fever, contracted while he was on a case at Rotherhithe. Mrs. Hudson says that Holmes has neither eaten nor taken any liquids in the last three days. Holmes forbids Watson to go near him because the illness is highly infectious. In fact, he refutes Watson and insults his abilities. Although Watson wishes to examine Holmes himself or send for a specialist, Holmes demands that Watson wait several hours before seeking help.

While Watson waits, he examines several objects in Holmes’s room. Holmes is angered when Watson touches things on his table stating his dislike for people fidgeting his things. At six o’clock, Holmes asks Watson to turn the gaslight on, but only halffull. He then instructs Watson to bring Mr. Culverton Smith from 13 Lower Burke Street to see Holmes but to make sure that Watson returns to Baker Street before Smith arrives. Watson goes to Smith’s address. Although Smith refuses to see anyone, Watson forces his way in.

Once Watson explains his duty on behalf of Sherlock Holmes, Smith’s assertiveness changes significantly. Smith agrees to come to Baker Street within half an hour. Watson excuses himself, saying that he has another appointment, and returns to Baker Street before Smith’s arrival. Believing that they are alone, Smith is frank with Holmes. It soon appears, to the hiding Watson’s horror, that Holmes has been sickened by the same illness that killed Smith’s nephew Victor.

At the end, Holmes calls for Watson to come out from behind the screen, to present himself as another witness to the conversation. Holmes explains his illness was feigned as a trick to induce Smith to confess to his nephew’s murder. Starving himself for three days and claiming to be suffering from a deadly infectious disease was to keep Watson from examining him and discovering the ruse, since, as he clarifies, he has every respect for his friend’s medical skills.

‘A detective’s perspective traps the criminal.’