Benjamin Manfred is a wealthy bookdealer who recounts to the Black Widowers the story of how he got his start in life. As a boy, he befriended an old bibliophile who had one extremely valuable volume in his library. Although he wouldn’t say which book it was, he did refer to it as “Triple Devil.” When he died, he left Manfred in his will any single volume of Manfred’s choice from the library, and Manfred is able to determine which of all those books was the truly valuable one.
The puzzle here is very weak, and means little to me personally since my own opinion of Charles Dickens (one of the “devils” of the story’s title) is rather lower than Asimov’s. This is, however, a true rarety among the Black Widower stories in that the puzzle is honestly a very minor part of the proceedings—the process of solving it takes only two pages, one of which is devoted to Henry’s correct solution. Rather, the story is about a man whose lifetime has been dedicated to books, and so Manfred emerges as an interesting and memorable character—and the end result is an unusually interesting and memorable Black Widower story.