Complex sentence: Angelo's first act is to begin the enforcement of an old law that makes fornication punishable by death, but proves himself a hypocrite when Isabella, the sister of Claudio, the first man sentenced under the law, comes to plead for her brother's life.
Split into simpler sentences: Angelo's first act is to begin the enforcement of an old law that makes fornication punishable by death. He proves himself a hypocrite when Isabella, the sister of Claudio (the first man sentenced under the law) comes to plead for her brother's life.