Major Nairn (Michael Byrne), Wellington's spymaster, arranges for another condemned soldier to be executed (keeping spectators at a distance so the switch can remain undetected), while he sends Sharpe and Sergeant Harper (Daragh O'Malley) to find out what is going on.
Meanwhile, Father Hacha (Nickolas Grace) and his brother El Matarife, Ducos' co-conspirators, abduct la Marquesa and imprison her in a nunnery to tie up loose ends.
The gloating Frenchman tells Sharpe that his duel and the murder of the nobleman has made it possible to negotiate a vital peace treaty with King Ferdinand VII of Spain; the British army will be forced to leave the country.
Harper and the rest of Sharpe's "chosen men" infiltrate the French prison in disguise and rescue their commander, just in time for him to play a pivotal role in the British victory at the Battle of Vitoria.
In his attempt to flee from the advancing British, the arrogant Ducos is hauled from his horse by the routed French soldiers and is shot and left to die (but survives to bedevil Sharpe in the future).