What is the action in act IV ?

The people are all gathered in the church to witness the wedding between Hero and Claudio. Leonato tells Friar Francis to hurry up. The Friar asks Claudio if he has come to marry Hero, to which Claudio replies, "No" (4.1.6). Leonato ignore the answer by playing with words to give it a different meaning, but Claudio interjects when asked if anyone knows why they should not be married. He tells Leonato, "Give not this rotten orange to your friend" (4.1.30) and accuses Hero of infidelity.