The Sacrifice. By Charlie Higson. 2013.496p. Disney/Hyperion, $17.99 (978142316565 I). Gr. 9-12.

This fourth, and apparently not final, book in The Enemy series finds yet more reasons to send members from various kid strongholds out into the "no-go zone," where the drooling, ravenous "sickos" seem to be developing a new kind of telepathic intelligence. But nine-year-old Sam is determined to join his sister in Buckingham Palace, so he takes to the lethal streets with two friends in tow, only to run across Higson's most unnerving character, religious nut Mad Matt, who believes that Sam is "the Lamb" that will lead the world from darkness. There's not much to differentiate teen leader Ed's subsequent rescue operation from similar sequences in previous volumes, and one is tempted to say the series is starting to generate diminishing returns. But the introduction of an intelligent sicko named Wormwood is a thrilling game-changer, and Higson once again impresses by largely avoiding sentimentality and romance to focus more realistically upon the "pulped, scabby, pus-oozing" threat. Onward we fight!--Daniel Kraus