A band of five young members of a rambler club journey into the Northwest to camp and visit a friend who has joined the Royal Northwest Mounted Police, but their plans are derailed when his absence becomes a worrying mystery. The boys, aided by scouts and a stern sergeant, ride through frontier country, meet villagers, confront stampedes and smugglers, and endure capture and perilous chases. Bold leadership, quick thinking, and loyal teamwork carry them through rescues and investigations until the mystery is resolved, with the youths gaining practical knowledge of mounted policing, wilderness survival, and mutual responsibility.