Ginevra, daughter of the King of Scotland, is betrothed to Ariodante. Polinesso, a jealous rival of Ariodante, wins the confidence of Ginevra's friend Dalinda. With Dalinda's unwitting help, Polinesso tricks Ariodante into thinking that Ginevra is his (Polinesso's) lover.
The King, hearing of Ginevra's alleged infidelity, disowns her, while Ariodante is reported dead by suicide. Polinesso then sends his agents to kill Dalinda, as the only witness to his plot. But Ariodante (whose suicide attempt was foiled), having met Dalinda while wandering in the woods, drives off the would-be assassins.
Polinesso, seeking to win the King's favour, now offers to defend the honour of Ginevra in a tournament. In the combat, he is mortally wounded by Ariodante's vengeful brother Lurcanio. Ariodante, having learned about Polinesso's plot from Dalinda, now appears and offers himself as Ginevra's champion. The dying Polinesso confesses his guilt and Ginevra is pardoned by the King.