Jason, rightful heir to the throne of Iolcus, is sent by his uncle Pelias, who has usurped the kingdom, on an errand meant to remove him permanently: retrieve the Golden Fleece, the hide of a magical ram, from the distant kingdom of Colchis at the eastern edge of the Greek world. Jason assembles a crew of the era's greatest heroes, the Argonauts, including Heracles, the musician Orpheus, and the twins Castor and Pollux, and sails aboard the specially built ship Argo, surviving a string of dangers along the way, including the clashing rocks of the Symplegades and the harassment of the blind prophet Phineus by the Harpies, which the Argonauts finally drive off in gratitude for which Phineus gives them crucial guidance for the rest of the voyage.
Arriving in Colchis, Jason finds King Aeetes unwilling to simply hand over the Fleece, and instead sets a sequence of trials meant to be fatal: yoking a pair of fire-breathing bronze bulls to plow a field, sowing the field with dragon's teeth that spring up instantly as fully armed warriors, and finally overcoming the sleepless dragon that coils permanently around the Fleece itself, guarding it without rest.
Among the Argonauts' earlier stops, the crew is briefly delayed on the island of Lemnos, whose women, having killed the island's men in a fit of collective anger at their infidelity, welcome the Argonauts warmly enough that the crew very nearly abandons the voyage there entirely before Heracles, who has stayed with the ship, shames them back into continuing toward Colchis.