After a prologue set in 1810, which introduces Major Brand (Mark Strong), a British officer serving with Richard Sharpe (Sean Bean), the plot fast-forwards to present-day 1813, where France is losing the war.
Wellington (Hugh Fraser) assigns them the task of blowing up a store of gunpowder vital to French General Calvet (Olivier Pierre).
As their joint mission unfolds, Sharpe realises that Brand is a traitor and French spy, luring them in order to trap Ross for his knowledge of Wellington's plans.
Fearing that Brand's influential friends may be able to overturn the verdict, Sharpe conducts an impromptu execution by pushing the traitor into a deep well.
The British blow up the gunpowder and escape, while Brand's men are given the opportunity to redeem themselves by acting as a rear guard to hold off the attacking French forces.