This is the only English-language biography of Carlos Kleiber, so it filled a most pressing need. Even so, the biography section is pretty scant (160 pages). This is followed by 18 pages of black and white photos (including photos of some of Kleiber's handwritten letters), and 116 pages of Kleiber's correspondence. Barber doesn't include his own letters to Carlos, but often explains the gist of what he wrote in order to clarify Kleiber's responses.
Barber doesn't include the small number of purely personal letters that passed between them, which date to the last year(s) of Kleiber's life. His original purpose in writing to Kleiber was to get conducting advice, which Kleiber was at first reluctant to give. But an epistolary friendship developed, which Kleiber seemed to value. He held back discussing his private life, mostly - never mentioning his wife in the letters. Between 1998 and 2003 Kleiber's letters got shorter and shorter and the published ones end with a November 2003 letter. In December 2003 Kleiber's wife died, so the purely personal letters probably contained information about that, and must have been raw and despairing, as his health was in decline too. He died in July 2004.
There is a cringeworthy deceit in Barber's correspondence: he creates a beard/girlfriend/partner for himself, Hilde, almost certainly because he's gay. There is a real Hilde, but she's married to another man. She was Barber's study partner in their doctoral program, and they were close friends. But Kleiber assumes Hilde is Barber's wife, and often sends his greetings and love to her in his letters. Barber explains that Hilde is not his wife; now Kleiber assumes they're "living in sin" (which he approves of). For nearly 15 years, Barber allows Kleiber to believe this fiction, "unchallenged by me because I was initially unsure of his attitudes, and afterward because it was too complicated to explain".
Kleiber was an extremely private and reclusive person, and you have to think he would have loathed having all of this personal correspondence published. But it would be hypocritical to complain about this violation of his privacy since Kleiber groupies so desperately wanted a peek behind the curtain into the mystique of his enigmatic genius. 5 stars because of the absolute rarity of the material.