Yesterday a person posted a description of the book on the Mahler-List:
"At first it seemed like a series of accidents plagued Vienna's Court Opera in the late spring of 1899. But after a singer is killed during rehearsals of a new production, the evidence suggests something much more dangerous. Someone is trying to murder the famed conductor and composer Gustav Mahler. Worse, Mahler might not be the first musical genius to be dispatched by this unknown killer. With the recent deaths of Johann Strauss and Johannes Brahms, it is feared that a madman is killing the great musicians of Vienna. Or, are these attacks spurred by Mahler's own dark past and his student friendships with composers Hugo Wolf and Hans Rott?"
It's definitely sounds fiction.