It's a swashbuckling romantic adventure when a duplicitous Spanish duke hires an Englishman to guard his unwilling Italian bride, a towering fighter who becomes known as the Swordsman of Siena. When Thomas Stanwood (Stewart Granger) defeats a whole group of attackers, their employer, don Carlos (Riccardo Garrone), the despised Spanish lord of Italian Siena, hires Stanwood to protect his fiancée, Orietta (Sylva Koscina). But when Stanwood learns that don Carlos murdered Orietta's father, he teams with the Italian beauty and a band of loyal partisans to overthrow don Carlos and wins the heart of the beautiful Orietta.