"Demetrius: A Play" by Friedrich Schiller

In a speech before the Polish diet Demetrius asserts his claim to the throne of the czars. He hopes for assistance from Poland. He declares that he is the son of Ivan the Terrible and was not, as reputed, murdered in 1591 as a child, but raised in a cloister and that he afterward was in the service of the Prince of Sendomir. He asserts that he is Czar Demetrius. His impressive speech convinces both the diet and the king. Although a formal resolution is not passed by the diet because of a veto by Prince Sapiehas, Poland goes into battle against Moscow. The Poles desire to oust Boris Godunov with the help of the upstart Demetrius. The forceful spirit behind the attempt is Demetrius' fiancée Marina, Mnischek's daughter, and Czar Ivan's widow. The latter has been banned to a cloister by Godunov and has for years been grieving for her allegedly murdered son when she receives the news that Demetrius is alive, after all.