When Napoleon escapes from Elba, Sharpe is settled in Normandy with Lucille, but his sense of duty recalls him to the army, and he is promoted to Lt. Col. in the 5th (Belgian) Light Dragoons, under the command of William, Prince of Orange. Sharpe and Lucille head for Brussels where the Duke of Wellington is based, with Lord John Rossendale and Jane Sharpe nearby in the city.
Out on reconnaisance, Sharpe sees a mass of French soldiers. He and the Prince's chief of staff, Rebecque, try to discover if it is a feint prior to Napoleon attacking Mons. Sharpe believes the French are heading to Quatre Bras, to split the Allied and Prussian forces. With French forces gathering, Sharpe knows he must tell Wellington and interrupts him at the Duchess of Richmond's ball. After delivering his message, Sharpe heads for the front, rejoined by Sgt. Harper (retired) and riflemen Hagman.
After the battle at Quatre Bras, Sharpe and Harper are given their post, the farm at La Haie Sainte. Woefully undefended, the men there repulse attacks from the French in bloody combat. The Prince of Orange has made mistakes, ending in the senseless loss of life of good soldiers. Eventually, Sharpe has had enough of this.
Not only must Sharpe deal with incompetent orders from the Prince of Orange, that lead to slaughter, he confronts his wife's lover, Lord Rossendale, in the midst of battle. The film climaxes as Wellington's small army 'holds the line' against Napoleon's veteran Imperial Guard.