King Idomeneus (Idomeneo) is overtaken by a storm as he returns to Crete from the Trojan Wars, and promises that is he is granted safe passage home, he will sacrifice to Poseidon the first living thing on dry land he sees. On the shore he meets Idamante, his own son. Horrified, the king instructs him to flee to Argos with Electra (Agamemnon’s daughter). Electra is in love Idamente and readily agrees, although Idamante is secretly in love with Ilia, the daughter of King Priam, a prisoner on Crete. Poseidon sends a sea monster to Idoeneo to remind him of his vow, but Idamante slays the monster. Ilia offers a sacrifice herself in Idamante’s stead and Poseidon relents.

The writing of Idomeneo was hampered by a number of difficulties – the poorly constructed libretto, the need to compose for a castrato, and the sixty-seven-year-old tenor in the title role who insisted that his arias be completely rewritten. There is much that is old-fashioned in the opera – arias are strictly segregated by passages of recitative and there are a number of coloratura arias which invite the singer to improvise, making the work one of Mozart’s few surviving operas conceived for celebrities who were out to impress.

Yet the opera is remarkable for its orchestral and choral writing and some passages, such as the storm in Act II and the Oracle scene, are of a richness unsurpassed by his later operas. Idomeneo was for many years overshadowed by Mozart’s glorious comedies but is today thought by many to be the greatest opera seria ever written.