At Westminster, Roberto is threatened with arrest for treason for his recent débâcle in Ireland, but Ehsabetta loves him and is determinded to save him, giving him a ring that will guarantee his freedom. Unknown to the queen, however, Roberto is deeply in love with Sara, who during his absence has been forced into a loveless union with his friend Nottingham, Later, Roberto visits Sara to say farewell, and he entrusts her with Elisabetta's ring, while she gives him a scarf in return.
The ministers of the queen are meeting to decide Roberto's fate. They have searched his apartments and bring the queen the scarf. When Nottingham sees it, remembering that he has observed his wife working on it, he bursts into a jealous rage. Deeply offended herself at this apparent evidence of Roberto's infidelity, the queen is furious. Roberto is sent to the Tower.
Nottingham confronts his wife, ordering her seclusion at home, thereby making it impossible for her to send the ring to Elisabetta. In the Tower, Roberto hopes he can restore Sara's reputation before he is executed.
At Westminster, Elisabetta is miserable, wondering why she has not received the ring, wanting Roberto to be spared. As a cannon shot announces Roberto's execution, Sara rushes in with the ring, followed by Nottingham, who declares he detained Sara so that he might have his revenge. The queen orders their arrest and then, haunted by visions of Roberto's ghost and her own demise, announces her abdication.