A mysterious flying creature glides above a ship at sea, clutching a shiny amulet. A crewman takes aim and shoots an arrow, causing the creature to drop the golden treasure. The crew deliberates over whether to discard the item, but Sinbad, the captain, is drawn to it. Upon examining the amulet, he is greeted by a vision of an enigmatic woman with an eye tattooed on her right palm. He decides to wear the amulet around his neck. That night, Sinbad is plagued by dreams of a man dressed in black who calls to him repeatedly, alongside the vision of the woman.
A fierce storm soon propels Sinbad's ship to the coastal town of Marabia. There, he catches a glimpse of the man from his dreams, who reveals himself as Koura, an evil magician intent on reclaiming the amulet, claiming it rightfully belongs to him. Sinbad narrowly evades Koura and encounters the Grand Vizier of Marabia, who has been ruling in the absence of a sultan. The Vizier, masked to conceal his disfigurement, explains that Sinbad's amulet is one part of a greater mystery; he possesses another piece. He regales Sinbad with the legend of the three pieces being the key to discovering the Fountain of Destiny hidden in the lost continent of Lemuria. Anyone who unites these pieces will be granted “youth, a shield of darkness, and a crown of untold riches.” Sinbad realizes the two pieces serve as a nautical chart leading to the Fountain.
Joining forces with the Vizier, Sinbad embarks on a quest for the Fountain. Koura, desiring the gifts from the Fountain for himself, is responsible for the Vizier's disfigurement. The creature that once dropped the amulet was Koura's minion, a magical homunculus that now spies on their movements, but it meets its end in a fit of destruction when captured.
As their journey unfolds, Sinbad encounters the vision of the woman from his dreams, a slave girl named Margiana. Her master, recognizing Sinbad's interest, offers him 400 coins along with Margiana in exchange for taking his son, Haroun, on the voyage to challenge him to grow up. Sinbad hesitantly agrees, and their adventure continues. Meanwhile, Koura enlists a ship and crew to pursue Sinbad, using dark magic that takes a toll on his vitality, visibly aging him each time he casts a spell.
Sinbad and his crew face relentless threats, including a wooden siren figure that Koura brings to life to seize their map to Lemuria. After a tense moment, Koura's minion attempts to thwart them but is ultimately destroyed by Haroun during an attack. The crew soon finds themselves captured by hostile natives, at which point Koura animates a six-armed statue of Kali to instill fear and mayhem among them. In a courageous confrontation, Sinbad and his men battle the statue, and Haroun's quick thinking leads to its destruction, revealing another piece of the puzzle in the remnants of the defeated figure.
However, they are soon captured by the natives who plan to sacrifice Margiana to their one-eyed centaur deity, the God of the Single Eye and the guardian of the Fountain. Koura manages to get to the Fountain of Destiny first, ultimately dropping one piece of the amulet into its waters to restore his life force. With his newfound power, he summons the centaur, leading to a fierce battle against the guardian griffin. Sinbad and his crew rush to the scene, where Koura’s machinations result in the griffin's demise.
In the climactic confrontation, Sinbad bravely slays the centaur, while Koura uses the second piece to turn himself invisible. During their duel, Koura’s invisibility gives him an advantage until he steps into the Fountain, rendering him a visible target for Sinbad to fatally strike. Upon dropping the final piece into the Fountain, a magnificent crown rises from its depths. Sinbad presents it to the Vizier, and as he dons the crown, the mask of disfigurement evaporates, revealing his true face. When Margiana questions why Sinbad did not keep the crown for himself, he responds, valuing his own freedom above all else.
