Cleaning out a closet, real or metaphorical, can be revealing. In the case of Samuel Barber’s sexuality, there was no closet. His lifelong relationship with Gian Carlo Menotti was established at a young age and never hidden from view; in fact, it was supported and encouraged by family and friends. The most important closet in Barber’s story was to be one emptied long after his death. A few years ago, a suitcase found in a closet during a building renovation was thrown into a dumpster and only rescued by workers in search of cash.

Fortunately, the contents of this suitcase found their way to Barbara Heyman, Barber’s preeminent biographer, for they were an astounding treasure trove of material relating to one of America’s most loved composers. These materials, along with other discoveries make the revision of Heyman’s seminal 1992 biography particularly engrossing. Happily, these developments coincide with a society more open and accepting of different sexualities.

Heyman’s describes her meticulously researched book as a “documentary study of [Barber’s] music,” using the words of Barber and those around him to tell the story and probe the artistic genesis of his works. While succeeding...