There's not much of a plot. Ryker catches his man early on but then beats him to a pulp in front of a crowd. He neglects to read his Miranda rights, too, so the killer is released on "a technicality," which infuriates Ryker. The killer eventually gets it, though, because Ryker makes sure of it. And it's very lovingly described.
So why did I even mention this one? Well, because it's the 5th book in a series, and the first ones were published under the name of Nelson DeMille. Before he became the mega-seller that he is today, DeMille wrote a lot of tough-cop paperbacks for the low-end paperback houses (this one's from Leisure Books), including the Keller series for Manor Books. DeMille revised the first two Ryker books and the Keller books and reprinted them with Pocket Books in 1989 under the name Jack Cannon, but with Keller's name changed to Ryker. So most likely he didn't write The Child Killer. I don't know who did. Maybe someone named Edson T. Hamill, or maybe that's a pseudonym. One thing's for sure: DeMille's bibliography is still a little cloudy.
The Child Killer is the kind of book that seems unlikely ever to find a publisher today. Not just because of the crude writing and the political incorrectness and the heavy-handed violence but because there's just no audience for it. There were dozens of these series in the '70s. Now they're all gone.
I wouldn't recommend reading The Child Killer, but it's an interesting curiosity.