Vincentio, Duke of Vienna, disgusted by the immorality in his city, announces his withdrawal from public life and leaves his deputy, the puritanical Angelo, in charge. Angelo, in his zeal for observing the letter of the law, begins a ruthless programme to stamp out sexual licence, in the course of which he condemns one Claudio to death. Surely Claudio’s virginal sister Isabella, a novice nun seeking mercy for her brother, could not awake the lust of this cold, censorious man?