The volume chronicles a critical sixteen-month phase of the Peninsular War, tracing the French advance into Portugal, the Anglo-Portuguese defensive measures—combining scorched-earth tactics, mass mobilization and construction of the Lines of Torres Vedras—and Masséna’s inability to breach those defenses leading to his retreat. It details the campaign actions around Bussaco and Torres Vedras, the logistical and partisan efforts that cut French communications, and concurrent French operations elsewhere in Spain including sieges and regional offensives. The narrative integrates official reports, private correspondence, and military papers to analyse strategy, troop dispositions and the conduct of commanders, supplemented by maps, appendices and newly published documentary material.