The city of Syracuse is tethered by conflict and war between the Byzantine Empire, with which it has an unstable truce, and the Saracen armies headed by Solamir. Not only is Syracuse exhausted by external war, but internal war as well; the soldier Tancredi and his family have been stripped of their estates and inheritances, and he himself has been banished since his youth. Two more noble families, headed by Argirio and Orbazzano, have been warring for years. Argirio and his family - his wife and his daughter, Amenaide - have been residing as guests of the Byzantine court, where Tancredi presides in exile. Also present in the court is Solamir, the Moorish general, who wishes for the lovely Amenaide's hand in marriage in hopes that he can create a Saracen-Syracusean alliance. However, Amenaide is secretly in love with Tancredi.

Act 1

Warring nobles Argirio and Orbazzano have agreed to a truce in the face of a greater threat: the approaching army of Solamir. The Senate has already given Tancredi's confiscated estates to Orbazzano, and now Argirio offers him his (Argirio's) daughter, Amenaide, in marriage. She dutifully consents to the arrangement, although she loves the exiled Tancredi. Soon, a letter she sends to her love falls into the hands of Orbazzano's agent near Solamir's camp. Amenaide has deliberately omitted Tancredi's name for his protection, and so it is assumed that the letter was intended for Solamir. A furious Orbazzano publicly reveals the letter at his own wedding ceremony, and Amenaide is sentenced to death for treason.

Act 2

Tancredi, who has returned incognito and offered his service to Argirio, believes that his love has been betrayed. Despite this, he challenges Orbazzano to a duel in defense of Amenaide's honor and life. He wins the duel, killing Orbazzano and winning Amenaide's freedom, before leading his fellow Syracusans into battle against Solamir.