The Case of the Gilded Fly, by Edmund Crispin
Woohoo! My mom turned out to have FIVE Crispin mysteries, so I am going to try to space them out. But I already read another one.
Professor Fen gets a new sidekick in the person of Nigel Blake, a journalist on holiday in Oxford (hoping to meet and date a certain actress). A prominent playwright is hoping to revive his career by putting on a new play, but tensions are thick between cast members, with minor actress Yseut Haskell at the center. When Yseut is found murdered in an impossible manner, Professor Fen is the only one who knows what's up.
The mystery was pretty good, with some interesting characters. I was sad that there were no goofy literary games this time, though. What bugged me about the story was how Yseut was treated throughout--but that was redeemed (somewhat, I think) in the end, as Fen realizes that Yseut's life was not less valuable than others.