Arlo Finch and the Rangers of Pine Mountain Company are headed to Camp Redfeather for two weeks of archery, canoeing, and investigating the ancient monster who lurks in the lake's icy waters.

But before they've even gotten on the bus, a major discovery puts Arlo, Indra, and Wu in jeopardy. Forces from beyond the Long Woods are after a mysterious item that only Arlo can recover. Meanwhile, the normally gentle forest spirits seem aligned against him.

New faces and sudden departures change the dynamics of the Blue Patrol. But it's the mystery of the long-lost Yellow Patrol that sends Arlo across the Lake of the Moon and into a thrilling new adventure. Once he uncovers the secret history Uncle Wade has been protecting, nothing will ever be the same.