Act I
The ten year long, Trojan War is over and the Greek armies have destroyed the Trojan nation. In Crete, everyone awaits the return of their King Idomeneo, from the war. Ilia, a captive Trojan princess in Crete, is torn between her hatred of her Greek captors and her growing love of Idamante, Idomeneo’s son. Electra, Agamemnon’s daughter, is in Crete where she found refuge after killing her mother. She is in love with Idamante and jealously observes the love that unfolds between Ilia and Idamante. Arbace, the King’s advisor, announces that Idomeneo’s ship has sunk and that the King is dead. Idomeneo however survives the storm as he vowed to Neptune that if the god saves him, he would sacrifice to Neptune the first person he would meet on shore. Idamante finds his father and once the king realized Idamante is his own son he pushes him away.
Act II
Idomeneo reveals his secret to Arbace who suggests sending Idamante far from Crete. Idomeneo decides to send his son with Electra back to Argos. Ilia confesses to Idomeneo that she has found a new father in him and he starts to suspect the love she feels towards his son. Electra believes that with Idamante beside her far away from Crete she will win him over. Idamante bids Ilia farewell but suddenly a storm arises. Neptune’s revenge is upon everyone.
Act III
Ilia yearns for Idamante’s love but opens her heart to him only once she realizes that his about to fight the monster that Neptune has sent to the island. Idomeneo does not answer his son’s questions about why he keeps his distance from him and orders Idamante to leave Crete and find refuge in a faraway place. Arbace announces that the people of Crete, led by the High Priest, demand their King to reveal the reason for the catastrophes falling upon the island. Eventually Idomeneo confesses, revealing that he has to sacrifice his son to Neptune.
Idomeneo and the people of Crete are praying as they prepare the sacrifice ritual. Arbace announces that Idamante has killed the monster and as he returns, the prince eventually understands the reason to his father’s behavior. Idamante in willing to fulfil his father’s vow to Neptune and as the ritual begins Ilia demands to replace him as the victim. Neptune’s voice is heard. The god agrees to revoke the vow as long as Idomeneo gives up the crown and makes Idamante and Ilia the new rulers of Crete. Everyone is happy aside of Electra who collapses.