After Eco, I want something a little less involved and faster-paced, so I am going with something by Gaston Leroux. Leroux's two most famous works are The Mystery of the Yellow Room, the most famous locked-room mystery novel of all time, and The Phantom of the Opera. The second will be the next fortnightly book.
Le Fantôme de l'Opéra was originally serialized in 1909 and 1910; it is based on both the history and legend of the actual Paris Opera House, although, of course, with plenty of literary license thrown in. Its popularity was quite extensive, but it became world famous with the 1925 production of the silent movie, The Phantom of the Opera. Multiple other adaptations followed, of varying quality. In 1986, of course, we got the Andrew Lloyd Webber musical.
Looking around, it looks like there were two classic radio adaptations, from Lux Radio Theater and CBS Mystery Theater, so I might compare them if I have the time.