Arlo Finch and the Rangers of Pine Mountain Company are headed off for two weeks at Camp Redfeather. But this summer camp is more than canoeing and hiking. It’s also a chance to search for ancient forest spirits, discover mysterious messages encoded in tree bark—and perhaps even encounter the ancient monster who lurks in the lake's icy waters. At camp, new faces and sudden departures change the dynamics of the Blue Patrol. And when Arlo and his best friends Indra and Wu stumble upon clues about the long-lost Yellow Patrol, Arlo uncovers a stunning history that leads right back to his very own family.