The Duke of Vienna takes some time off, leaving the government in the hands of his deputies, Escalus and Angelo. They enforce the sexual purity laws which had fallen into disuse; the brothels all close (leading to much grumbling from former staff and clients) and one Claudio is condemned to death for impregnating his girlfriend. Claudio's sister Isabella pleads for his life: Angelo promises to spare him in return for sexual favours from her. The Duke, who actually hasn't gone away at all but is hanging around disguised as a monk, persuades Isabella to go along with the plan but finds Angelo's brutally dumped ex-fiancee to take her place in his bed. There is a grand final scene in which All Is Revealed, Angelo is forced to marry his ex, Claudio is released and the Duke gets to marry Isabella.
I imagine that in its original environment, this worked rather well: the Duke is an enlightened ruler who exposes his deputy's flaws, rights an old wrong, and ameliorates the effects of bad laws. To today's audience, it's a much more difficult sell: the Duke is a manipulative bastard who could actually have resolved it all by Act 2, but instead humiliates pretty much everyone else in sight in order to assert his authority. The enforced marriage of Angelo to his old flame also works less well today. It would be interesting to see this done with the Duke deliberately portrayed as the villain. The Cambridge student production I saw didn't do that but did end with Isabella bluntly though silently rejecting him.
Arkangel take a difficult script and do it well, with Roger Allam, one of their star performers, as the Duke, Simon Russell Beale as Angelo, and Claudia Gonet, a new name to me, as Isabella; the veteran Christopher Benjamin (Inferno / Talons of Weng Chiang / The Unicorn and the Wasp) is Escalus.
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