By Its Cover is the much anticipated twenty-third instalment in Donna Leon's bestselling crime series, where Commissario Brunetti is better than ever as he addresses questions of worth and value alongside his ever-faithful team of Ispettore Vianello and Signorina Elettra. When several valuable antiquarian books go missing from a prestigious library in the heart of Venice, Commissario Brunetti is immediately called to the scene. The staff suspect an American researcher has stolen them, but for Brunetti something doesn't quite add up.

Taking on the case, the Commissario begins to seek information about some of the library's regulars, such as the ex-priest Franchini, a passionate reader of ancient Christian literature, and Contessa Morosini-Albani, the library's chief donor, and comes to the conclusion that the thief could not have acted alone. However, when Franchini is found murdered in his home, the case takes a more sinister turn and soon Brunetti finds himself submerged in the dark secrets of the black market of antiquarian books. Alongside his ever-faithful team of Ispettore Vianello and Signorina Elettra, he delves into the pages of Franchini's past and into the mind of a book thief in order to uncover the terrible truth.