In September 1792, Paris is consumed by the Reign of Terror, where the guillotine claims countless noble lives daily. Rumours sweep the city about the Scarlet Pimpernel, a mysterious English leader of a secret league who continually outwits the revolutionary tribunal and saves aristocrats from execution. Meanwhile, in England, the brilliant and fashionable Lady Blakeney navigates a chilly estrangement from her seemingly foolish husband, Sir Percy. Unaware that Percy leads the secret league, Marguerite struggles with a lonely marriage and her own past regrets.
Complications arise when Chauvelin, the ruthless agent of the French Republic, arrives in England determined to unmask the Scarlet Pimpernel and destroy the rescue network. Blackmailed by Chauvelin through her beloved brother Armand, Marguerite is forced to betray the league's secrets. Upon discovering that her husband is the very hero she helped expose, Marguerite rushes across a storm-tossed Channel to warn him of the fatal trap awaiting him in France.
