These three chapters see rapid developments in events upon the moor. Watson, holed up at Baskerville Hall, continues to write reports to Holmes, who as far as he knows is busy working on the case in London. In Chapter 11 Watson learns from Barrymore, the butler, that another man as well as the escaped convict Selden (Barrymore's wife's brother) is living secretly out on the moor. Selden has seen him. Watson also learns that the late Sir Charles Baskerville had a secret assignation with a lady called Laura Lyons, on the night of his death. These two revelations give Watson plenty of food for thought.
In chapter 11 Watson manages to secure an interview with Laura Lyons, who turns out to be the estranged daughter of the cranky old Frankland, one of the Baskerville neighbours. She was going to meet Sir Charles because she was needing financial assistance and he had agreed to help her. However, she ended up not going. Watson is still puzzled as to her exact role in the affair, but his attention is diverted to finding out more about the second man on the moor. He goes to lie in wait for him, and is utterly astounded when this man turns out to be Sherlock Holmes, whom he thought was in London.
In chapter 12, Holmes reveals all he has been doing. He thought it would be more useful if he came to work secretly on the case upon the moor itself. Watson is rather indignant at having been tricked thus, but Holmes assures him that his reports have been very helpful. Holmes of course has found out plenty for himself. He has established that Laura wanted money to get a divorce. It turns out that Stapleton has acquired a hold over her and she actually is wanting to be divorced from her first husband in order to marry Stapleton. But Holmes's most startling revelation is that Miss Stapleton is in fact, Mrs Stapleton - Stapleton's wife and not his sister. Holmes has learned that Stapleton is in fact the chief villain of the whole business.He has been pretendng that his wife was his sister in order to attract Sir Henry to her and eventually lure him to his doom. Watson is shocked at the extent of Stapleton's schemes. Suddenly a terrible cry sounds from the moor. The hound has struck again. Watson and Holmes rush to the spot and at first think it is Sir Henry who has been killed, but it turns out to be Selden, dressed in Sir Henry's old clothes, given him by Barrymore. Stapleton also arrives. He pretends to be shocked at what's happened, but Holmes and Watson see that really he's disappointed that the victim was not Sir Henry.