To my surprise, it has seemed almost easier to find children's books than adult novels referencing opera. Two notable examples are The Bear Who Loved Puccini (investigation reveals that it is about a bear who hears Madame Butterfly on the radio (?) and decides to become an opera singer (?!), and is successful in his quest to do so (!!!) ) and a picture book called Pet of the Met, which was written by none other than Don Freeman, author of Corduroy. Apparently, the eponymous hero is a mouse who turns the pages for the Met's prompter, avoids the designs of a neighborhood cat, and really loves Mozart, especially Die Zauberflöte. This I may have to look up. The Metropolitan Opera gift shop (though not their online outlet) also has gorgeous picture book renditions of several operas. Now, I would give my youngest cousins a picture book of Barbiere or Cenerentola or L'Elisir d'Amore in a heartbeat; however, adaptations of Turandot and Madame Butterfly (not to mention Cavalleria Rusticana!) I find rather creepy, despite the gorgeous illustrations.
Tenor of Love is a novel which I pursued despite its title, which wouldn't seem out of place on a Lilian Gish film. Written from the imagined perspectives of the Giachetti sisters and Dorothy Benjamin, it covers Caruso's life from the beginning of his musical career to his death. The author is a poet, to which I attribute a prose dedicated to details of atmosphere. The romantic anxieties, hopes, and liaisons would not have disgraced a Lilian Gish film either... but I don't mind the occasional equivalent of a 1920s melodrama in my reading list, and I learned some things about opera performance in the early twentieth century, so it was rather fun, if not particularly substantial.
Among the many things I enjoy about Donna Leon's popular series of mystery novels set in contemporary Venice is the inclusion of excerpts from libretti (mostly Mozart's) at the front of each book. Guessing their thematic relevance is delicious fun. The first in the series (and, caveat lector, one of the most disturbing, in my opinion,) Death at La Fenice, even revolves around the personalities of an opera house. Murder during La Traviata (gasp!) sets off an investigation which goes behind the scenes and plays with stereotypes and archetypes in interesting ways.
The hilarious, often genre-parodying mystery novels of Edmund Crispin include Swan Song which, in a much less serious vein than Leon's novel, focuses on a shortly-post-war performance of Meistersinger in England. Among the many humorous touches, my favorite was probably the running joke about the obliviously abrasive personality of the man singing Beckmesser, but the entire thing was one of those books which obliges one to hoot with laughter and read juicy paragraphs aloud to any friends in the vicinity. I have also recently heard of a series of mystery novels taking place in eighteenth-century Venice with a castrato as their protagonist. Now, this sounds as though it could be tremendous fun (it had me at eighteenth-century Venice!) but I am not unaware of the potential for heavy-handed disaster. Interrupted Aria is the title of the first book in the series... explore at your own risk, Gentle Readers, or do tell me what you think if you know them!
By far my favorite opera-related novel so far is Bel Canto, by Ann Patchett, which I picked up and put down again countless times in bookstores, put off by dreadful blurbs. Prominently featured on the cover was a reviewer's claim that the book "is its own universe," which I found a declaration both cryptic and pretentious. And the back cover made much of the fact that the entire thing took place in a hostage situation in South America, described by the New Yorker as "a fantasia of guns and Puccini and Red Cross negotiations." Terrible!! I thought. But I quote these alarming assessments only to contrast my own, which was that, actually, it was a beautiful novel which managed to have its realistic tone describe not only situations of more or less cynical compromise, but also glorious moments, events, and relationships made possible by music. And I loved the novel's celebration of the fact that opera can be one of those things that makes one feel the miraculous is possible.
Update: no sooner do I complain of not finding enough opera-related novels than lo, La Cieca calls for a book group! The suggested first novel is a pastiche of which I had never heard, but which appears to inspire enthusiasm.