La Ruta narrates Barea's military service and his participation in the Rif War in the Spanish Protectorate of Morocco. The book focuses on the events preceding and following the disaster of Annual; detailing the incompetence and corruption of the Spanish military leadership, and the lack of training and preparation of the conscripted Spanish troops who have to endure the harsh conditions of colonial warfare. Barea himself served in a regiment of military engineers, reenlisting as a regular and being promoted to the rank of sergeant.