In this tale, Holmes is investigating the disappearance and suspected murder of Neville St. Clair, a prosperous and respectable business man. Every day he travels into London to work; one day his wife goes into the city separately to shop. Passing by a known opium den, Mrs. St. Clair glances up at it distastefully and is shocked and horrified to see her husband in an upstairs window. He disappears immediately and Mrs. St. Clair, unable to convince the doorman to let her in, summons the police, convinced that something is terribly wrong. The police search the premises but cannot find St. Clair. The room in which Mrs. St. Clair is certain she saw her husband is occupied only by a well-known local beggar, Hugh Boone, who has a facial deformity. The police search him and find him in possession of a few of St. Clair's personal items including his coat which, oddly, has its pockets stuffed full of small change- pennies and half-pennies.
The police take Hugh Boone into custody on suspicion of murder but he refuses to say anything, or to even wash while he's being held at the prison. Mrs. St. Clair asks Holmes to look into the case, which he agrees to do. Originally assuming that St. Clair is dead, Holmes must revise his thinking when, several days after his disappearance, Mrs. St. Clair receives a letter from her husband- in his own handwriting- which asks her not to worry and also contains his wedding ring.
Holmes- naturally- figures out what's going on and makes his way to the jail (with a bemused Watson in tow) to see Hugh Boone. Watson notes that Holmes is carrying a Gladstone bag with him. Arriving at the prison, they find Boone asleep in his cell. Holmes seizes the opportunity; opening the bag, he pulls out a bath sponge and proceeds to wash the man's face. It turns out that Boone's facial deformity- twisted lip and all- is merely an expert make up job and Boone the beggar is, in actual fact, Neville St. Clair. If you want to know what he was doing and why, you'll have to read the story- it's well worth it!