Ion, the son of Apollo and the Athenian princess Creusa, is abandoned in a cave on the Acropolis and is taken by Hermes to Delphi.

Later, Creusa, married to Xuthus, is unable to conceive and visits Delphi to consult the oracle. She is told that she must adopt the temple's new servant.

Creusa refuses and tries to kill him, until it is revealed that he is her son Ion. With the intervention of Athena, they take him to place him on the throne of Athens.