Mrs. St. Clair is convinced that she momentarily saw her husband, a respectable journalist who commutes to London from their country home, looking out of the window of an opium den in a rough part of the city. The police investigate but find a bundle of clothes and no body. Mr. St. Clair is not dead but Hugh Boone, a literate beggar given to quoting the classics, knows exactly where he is and so - eventually - does Sherlock Holmes.