When sixteen-year-old Noah Keene runs away from his home on the Oregon coast, his quest for a sense of belonging becomes a headlong race to save his younger sister - and the world - from monsters he thought existed only in nightmares. Trapped in endlessly twisting caverns inside Humbug Mountain, Noah must find Abby and survive a series of challenges. With the help of a mysterious hermit, a skeptical girl-warrior and a one-armed wizard, he has to seal a portal in the earth before the demonic troll, Spid, and his army can pass through.