CASIMIR, a brother of LODOISKA, a young Polish lady, who has been secretly and hopelessly attached to Demetrius, in the house of the Waywode of Sendomir, has, at his sister's request, accompanied Demetrius in the campaign, and in every encounter defended him bravely. In the moment of danger, when all the other retainers of Demetrius think only of their personal safety, Casimir alone remains faithful to him, and sacrifices life in his defence. The conspiracy breaks out. Demetrius is with Marfa when the leading conspirators force their way into the room. The dignity and courage of Demetrius have a momentary effect upon the rebels. He nearly succeeds in disarming them by a promise to place the Poles at their disposal. But at this point SCHINSKOI rushes in with an infuriated band. An explicit declaration is demanded from the ex-empress; she is required to swear, upon the cross, that Demetrius is her son. To testify against her conscience in a manner so solemn is impossible. She turns from Demetrius in silence, and is about to withdraw. "Is she silent?" exclaims the tumultuous throng. "Does she disown him?" "Then, traitor, die!" and Demetrius falls, pierced by their swords, at Marfa's feet.