Eight years after he was locked up for snapping the neck of a 2-year-old girl, Rand Duchay, newly released from prison, puts in an anxious phone call to Alex Delaware, the affable L.A. shrink/sleuth Jonathan Kellerman has been writing about since 1985's When the Bough Breaks. ''I'm not a bad person,'' Rand says. But before he can explain himself further, someone shoots him in the head. Kellerman introduces some colorful characters in this enjoyable, disposable mystery, including Rand's smarmy and hypocritical ''spiritual advisors'' and an uncommonly odious lawyer. But like too many contemporary thriller writers, Kellerman has built Rage around an impossibly grotesque villain. Clearly, it's easier to cook up a crass, stomach-turning criminal than a suspenseful and believable plot.