King Oebalus of Lacedaemonia and his son, Hyacinthus are preparing a sacrifice to Apollo when their altar is struck by a bolt of lightning. Apollo himself arrives to offer his friendship to young Hyacinthus and love to his sister, Melia. Melia's euphoria over the prospect of marrying a deity is shattered, however, when Zephyrus runs in to report that Apollo had killed Hyacinthus with a discus. But just as Zephyrus is finishing his story, Apollo himself blows in and sends the liar off with a blast of the west wind. The distraught Melia doesn't know what to believe and shuns the god as she leaves to find her brother.
As it turns out, Hyacinthus manages to identify Zephyrus as his killer to his father as he expires. Oebalus and Melia sing a duet of grief that so touches Apollo that he turns the boy's body into the flower hyacinthus (with its signature marking), and reaffirms his love for Melia who prise the power of Numen.