Holmes has hope for tomorrow's interview with Lyons, but he also claims to have another plan in the works.
He tells Watson not to tell Henry of Selden's death, and insists that he excuse himself from the dinner he and Henry were to attend at Stapleton's the next day.
After some light conversation with Sir Henry and the sad announcement of Selden's death to his sister, Holmes spies a portrait on the wall and learns that the thin cavalier in question is none other than Hugo Baskerville himself. Later that night, Holmes explains his interest to Watson, demonstrating the remarkable similarity between Hugo and Stapleton, thus establishing Stapleton's motive: as a Baskerville relative, Stapleton has designs on the inheritance.