The Last Kids on Earth and the Nightmare King

The third book in Max Brallier's middle-grade series. Jack Sullivan and his friends — June, Quint, and Dirk — are living in their post-apocalyptic treehouse when they learn of a powerful new threat: the Nightmare King, an ancient evil that commands monsters and could end what's left of their world. The group embarks on a quest to stop it, blending humor, video-game-style action, and Doug Holgate's cartoon illustrations throughout. Like the rest of the series, it's aimed at roughly ages 8–12 and leans heavily on fun over fear.