Idomeneo, the King of Crete, is returning to Greece after years away at the Trojan War. On his way home, his ship sinks and he survives only due to the grace of the god, Neptune. In return, Idomeneo agrees to sacrifice the first mortal he finds. It so happens that the first mortal that rushes to see him is his own son, Idamente. Previously, to the dismay of Elettra, Idamente has fallen in love with Ilia, a Trojan princess. As Idomeneo is about to allow his own son to be sacrificed, Neptune intervenes and allows Idamente to survive as long as he is allowed to take over the thrown in place of his father.