This is the final novel in Yukio Mishima's landmark Sea of Fertility tetralogy. The four novels trace the life of Shigekuni Honda, and his life-long obsession with a friend who dies in their teens and who he believes in reincarnated in three young people he encounters at various stages in his life.
In The Decay of the Angel, Honda is almost 80 years old and happens upon the young Toru who bears on his skin the signs that he is the latest reincarnation of his friend - three moles peculiarly placed and arranged on his chest. Upon meeting Toru and realizing who he is, Honda decides he'll adopt the boy. I'm sure things can only go wrong from here on in, given what happens in the previous three books and given that both Toru and Honda are construed as the embodiments of evil (Mishima's word! Well, at least, the translator's word).
The other thing is this: I find it disturbing to be reading a novel which I know culminated in Mishima's suicide - indeed, which Mishima always planned would end with him disemboweling himself. Because Mishima killed himself immediately upon finishing this novel, it was not edited - just as the previous three were unedited before publication.
I can't help but wonder how the knowledge of his impending death effected the writing of the novel. It would be too obvious to say that the characters' obsession with death reflects Mishima's own, for death figures heavily in all his works (the ones I've read anyhow) and in this tetralogy it's absolutely necessary. Perhaps we can see Mishima's consciousness of his fate in Toru's constant awareness of the existence of another world just beyond his vision, and his concomitant sense of barely existing in this one.