What information does the cabman gives Sherlock Holmes -Why Holmes feel checkmate?

That evening, Watson and Holmes receive two telegrams. The first is a return telegram from Barrymore, suggesting that he is indeed at Baskerville Hall. The second reports that Cartwright has been unable to find the cut sheet of the newspaper.

At that moment, the cab driver, whom Holmes had sent for earlier, appears at the door. He tells Holmes that the bearded man had claimed to be a detective, and had told him to say nothing to anyone. Strangest of all, the man had claimed to be named "Mr. Sherlock Holmes" (188). Holmes is surprised and amused.

He pays the cab driver for details of the day's journey, and then sends the driver away. Noting that "our third thread" has snapped, Holmes admires his adversary as "worthy of our steel" (189). He then wishes Watson luck in Devonshire, noting that this case is proving to be an ugly business.