This is another solid entry in Phaidon's 20th Century Composers series -- heavy-stock paper and great photos (including one of his first performance of "Peter and the Wolf" for a group of children) add to Jaffe's text. Jaffe offers the best answer I've found (searching through several books) to the question of why Prokofiev returned to Russia at the height of Stalin's terror. Apparently it was a combination of homesickness, vanity, political naivete, and aesthetic theory. The Soviet regime promised Prokofiev an exceptional privileged status, which appealed to his vanity -- he was overshadowed by Stravinsky in the West, where he never felt he was properly appreciated. And the turn to "social realism," forced on Soviet artists by Stalin, coincided with Prokofiev's voluntary turn away from modernism toward simplicity, melody, and populist narratives. I enjoy both the early and late Prokofiev, but I can see the point of those who claim that his later works are more accomplished. While his music is not on the cutting edge, and thus he was never a critics' darling, Prokofiev's music is marvelous.
This is the best single book available at the moment for anyone who wants to know more about one of the greatest early 20th century composers!