When the opera begins, Paolo, the leader of the Plebeian party, persuades Pietro to encourage the plebeians to vote for Simon Boccanegra as the new doge of Genoa. Boccanegra arrives and agrees that he would be doge if he were chosen. Simon thinks this would make Fiesco allow him to marry Maria. For the past three months Fiesco has locked his daughter in the palace because she had had a child with Simon.