Realm Guard: Rangers of the North is an unofficial Mouse Guard campaign hack set in Tolkien's Middle-earth. Players are Dúnedain, Rangers of the North, undertaking dangerous missions in Middle-earth during the Fourth Age. The book gives an overview over the Dúnedain and their duties and over the lands of Middle-earth. It introduces the Strained condition as a replacement for Mouse Guard's Sick condition, presents the Hazards of the setting, defines the Nature of the races of Middle-earth, and lists descriptions and statistics for denizens, allies, and enemies. The Mouse Guard food chain is replaced by the Scale of Might. Character creation is supplemented by new skills, traits, gear, and wises. The book includes some Ranger characters and a sample mission called The Trouble in High Pass.