Pelias, portrayed by Douglas Wilmer, ascends to the throne of Thessaly by committing the heinous act of murdering King Aristo. Yet, amid the chaos and bloodshed, a prophecy looms ominously over him: he will one day meet his downfall at the hands of a child of Aristo, a child who will bear the telltale mark of wearing one sandal. In a twisted turn of events, Pelias eventually kills one of Aristo's daughters after she seeks sanctuary from the goddess Hera, thus sealing his enmity with the powerful deity.
Fast forward two decades, and we meet Jason, played by Todd Armstrong, the son of Aristo, who has matured into a young man. In a fateful encounter, Jason unknowingly saves Pelias's life, losing a sandal in the process. While Jason is blissfully unaware that he has just rescued his father's killer, Pelias, who recognizes his nemesis, decides to keep his identity hidden. However, he cannot eliminate Jason outright, as his own demise is also prophesied should he do so.
As whispers of Jason's daring quest to retrieve the illustrious Golden Fleece resound throughout the land, Pelias subtly encourages him, secretly hoping that the perilous journey will lead to Jason's demise. A multitude of brave men from across Greece vie for the honor of joining Jason on this epic adventure. The ship they voyage on, named the Argo in homage to its builder, Argos [Laurence Naismith], eventually earns the group the title of Argonauts. Among the chosen is the demigod Hercules, interpreted by [Nigel Green], alongside Acastus, portrayed by [Gary Raymond], who, unbeknownst to Jason, is still obedient to Pelias and tasked with sabotaging the mission.
As their saga unfolds, Jason is taken to the heights of Mount Olympus by Hermes, played by Michael Gwynn, where he is granted an audience with the mighty gods Zeus and Hera. Hera expresses her hopes for Jason's success but reveals that Zeus has limited her ability to intervene directly in mortal affairs. It is here that Jason learns he can invoke Hera's assistance only five times, signifying the connections between mortals and the gods in their unfathomable game of power. Hera, in response to Jason's silent inquiries, guides him toward the Fleece located in the distant land of Colchis.
Throughout their treacherous expedition, myriad threats await the Argonauts. As supplies dwindle, Jason turns to Hera for guidance. She directs them to the Isle of Bronze, cautioning Jason to take only provisions. However, a reckless chase after goats leads Hercules and his youthful companion Hylas, played by John Cairney, to stumble upon a hidden chamber replete with treasures belonging to the gods, topped by the colossal bronze sentinel, Talos. Ignoring Hylas's warning, Hercules secures a gigantic brooch, inciting Talos to spring to life and unleash chaos upon the crew. In a gripping clash, Jason manages to extinguish the wrath of the sentinel using Hera's insight. However, tragedy strikes when Hylas vanishes and is presumed lifeless, leaving Hercules disheartened and determined to search for him, forcing the crew into a heart-wrenching dilemma.
Ultimately, Jason makes one last appeal to Hera as circumstances compel them to leave Hercules behind. Hera’s confirmation of Hylas’s fate is a bitter pill to swallow, signifying the sacrifices that come with their perilous journey. In search of further guidance, Hera urges them to meet Phineas, played by [Patrick Troughton], a blind seer plagued by Harpies sent by Zeus as punishment for his past transgressions.
Upon their encounter, Phineas, grateful for their intervention against the tormenting creatures, imparts crucial knowledge regarding their course to Colchis, entrusting Jason with his lone possession—an amulet of great significance. Their journey, however, is fraught with even more peril as they must navigate the treacherous Clashing Rocks, an area notorious for engulfing ships whole. Miraculously, another vessel's doomed attempt to traverse the strait serves as a warning, and as despair sets in, Jason discards Phineas's amulet into the water—a divine moment transpires when Triton emerges, holding back the rocks just long enough for the Argo to safely pass.
Upon arriving in Colchis, their fortunes take a dark turn when mistrust arises among the crew, culminating in a fight between Acastus and Jason. After a fleeting skirmish, Acastus makes a daring leap into the sea to escape, fooling his companions into believing he has perished. Believing the threat subdued, they gratefully accept an invitation from King Aeëtes, played by [Jack Gwillim], for a grand feast. Yet, the treachery of Acastus, who divulges their intentions, sees them swiftly captured.
In a twist of fate, it is the cunning Medea, enacted by [Nancy Kovack], who aids in their escape from the clutches of Aeëtes. Acastus's nefarious intentions lead him to covet the Fleece for himself; however, he ultimately meets his end at the hands of the Hydra, its wrath sealed in the annals of their treacherous endeavor. Jason, rising to the occasion, confronts and eliminates the monstrous beast, seizing the coveted Fleece. Yet the king has not relinquished his pursuit. In a desperate act, Aeëtes scatters the Hydra's teeth, sowing chaos as they awaken, transformed into menacing skeletons that hunt Jason and his comrades.
In a groundbreaking sequence of special effects that took Ray Harryhausen a staggering four and a half months to create, the battle unfolds—a true testament to the artistry of filmmaking. Faced with overwhelming odds, Jason leaps off a precipice into the sea, narrowly escaping destruction. With their mission accomplished and the Fleece in hand, he, Medea, and the surviving Argonauts set sail for home, the weight of their trials forging an unbreakable bond among them as they brave the journey back to Thessaly.
