'Caligula is not a madman,' says composer Detlev Glanert, 'but rather an intelligent, rational creature who skilfully experiments with human beings, just like Stalin or Hitler.' Glanert bases his opera on Albert Camus' play. The Roman emperor Caligula's descent into madness is sparked by the death of his sister and lover, Drusilla.

The opera depicts the ways in which Caligula's challenges to those around him test the boundaries of their loyalty to the office of emperor, to him personally, and to each other. Demanding that his former slave Helicon brings him the moon, he enacts absurd and brutal laws. He rapes the wife of one of the senators and forces another to drink poison; appearing at some festivities as Venus, he decides to marry the moon, commanding his guests to worship him. Summoning four poets to entertain the assembly, he arbitrarily sentences them to death; the guests are provoked into conspiring to kill him, but Caligula tricks them with false news of his own demise. His wife Caesonia proposes her own death, at his own hands, as the ultimate proof of her love; the conspirators finally put Caligula to death.