Crispin published the Fen novels from 1944 to 1979, and certainly Fen is, in many ways, straight out of the golden age of the British amateur detective tradition. Somehow, the police tolerate and even accept the work of an amateur untrained in police work, allowing him to interview witnesses on his own and somehow never scolding him for, say, moving the body before the police arrive. Oh, yes, I did grimace at that.
Swan Song is built around the rehearsals for a production of Die Meistersinger, the first postwar British production, in fact, circ 1947. Crispin gets most of the musical details right, although I am dubious about the existence of a tenor who sings both Ernesto in Don Pasquale and Walther in Meistersinger, not to mention the soprano whose repertory includes the Marschallin (accent on the third syllable), Salome, Eva, and....Mimi? Well, she's English, so who knows. Eva Turner's early career included Musetta!
And of course in a book called Swan Song that's about murder and Wagner, the opera should be Lohengrin.
But the best musical bit is this; it is completely unrelated to the plot and funnier in context:
...A few new-comers drifted in and uttered reluctant apologies to [the conductor]. The tuba-player arrived, unpacked his instrument, and began making a sound like a fog-horn on it, while the rest of the orchestra chanted "Peter Grimes!" in a quavering, distant falsetto.