After the British army's escape at Corunna, the war against Napoleon's forces in Iberia turns even more brutal. The film opens with the siege of Saragossa, where French troops try to break Spanish resistance street by street, then follows the arrival of a new British commander, Sir Arthur Wellesley, the future Duke of Wellington. It traces his crossing of the Douro River to retake Porto, his victory at Talavera, and the secret construction of the Lines of Torres Vedras, the fortifications built to shield Lisbon from French attack. Historians walk the ground where these campaigns happened, using maps and battlefield detail to explain how British discipline combined with a new kind of warfare, the Spanish guerrilla resistance, to grind down a French army that occupation had left exposed and afraid. The episode treats Wellington's rise less as inevitable triumph than as a close, improvised fight, one where fortification and irregular resistance mattered as much as any pitched battle.