The ballet opens on an autumn morning in Germany. Giselle and Albrecht are in love. Hilarion is in love with Giselle, too. She does not love him though. He grows jealous. He promises to take revenge. Albrecht's gentle manners arouse Hilarion's suspicions. Albrecht is really a Duke. He is pretending to be a peasant. The peasant boys and girls start a waltz. Giselle asks Albrecht to dance with her. Giselle's mother says her daughter has a weak heart. She will die if she does not give up dancing. She is afraid that Giselle will become one of the Wilis. The Wilis are ghostly female spirits. They dance men to death.