So Just and Glorious a Cause is a highly detailed narrative of Wellington's first campaign in the Peninsula. Using memoirs, letters, and previously unpublished primary sources, it covers events from Junot's invasion in late 1807 to the Portuguese revolts in the summer of 1808, and then the sailing of the British expedition and the battles of Roli a and Vimeiro, through to the controversial Convention of Cintra and the liberation of Portugal from the French.

In 1807, with most of Europe under his control, Napoleon looked towards the Iberian Peninsula, hoping to complete his hegemony and extend his reach to South America. He sent one of his most loyal generals, Jean-Andoche Junot, with 25,000 men, to conquer Portugal. The Portuguese had long been caught in the middle between Britain and France. Faced with an invasion he had little hope of preventing, the Prince Regent fled to Brazil, assisted by a Royal Navy squadron, and let his country be occupied.

In the summer of 1808, with the rebellion of the Spanish and Portuguese people spreading across the Peninsula, Britain sent an expedition to liberate Portugal under Sir Arthur Wellesley, the future Duke of Wellington. Still a relatively junior and unknown commander, Wellesley fought an aggressive and successful campaign. He defeated the French first at Roli a and then at Vimeiro but was prevented from sealing his victory by the arrival of more senior officers. The French negotiated generous terms in the Convention of Cintra and were evacuated back to France, ending their occupation of Portugal.

So Just and Glorious a Cause makes extensive use of primary sources from all levels of the French, Portuguese and British forces involved, many of them previously unpublished. The terrible forced marches of the French troops as they crossed the border into Portugal, the frenzied diplomatic efforts in Lisbon, the subsequent brutal occupation, and the Royal Navy blockade are all examined, as well as Vice Admiral Cotton's efforts to fan the flames of revolt in Portugal and offer support for the uprisings. The French, Portuguese and British forces are analyzed in detail, as are the logistical challenges of Wellesley's campaign. The narratives of the first skirmish at Obidos and then the battles of Roli a and Vimeiro are constructed from first-hand accounts from both sides, and many misconceptions about each action are addressed. Finally, numerous myths surrounding the controversial Convention of Cintra are tackled, including Wellesley's part in the negotiations.