Creusa returns to the temple gate accompanied by her father's elderly tutor. Sensing that something is amiss, Creusa presses her maids to tell what they know. They reveal that Apollo gave Ion to Xuthus as a son while she will remain childless. The old tutor speculates that Xuthus discovered that Creusa was barren, sired the child by a slave, and gave him to a Delphian to raise. The old man tells Creusa that she must not allow the bastard child of a foreigner to inherit the throne. Instead, she must kill her husband and his son to prevent further treachery. He volunteers to help her. The servants pledge their support.