In 1936, Doc Savage returns to New York City after a visit to his top-secret Arctic hideaway, the Fortress of Solitude, and soon learns that his father has died under mysterious circumstances while exploring the remote interior of Hidalgo. While poring over his father's papers, the investigation takes a dangerous turn when an assassination attempt targets him, forcing a tense chase that ends with the would-be killer plummeting to his death on the edge of the Eastern Cranmoor Building. The fallen sniper’s body bears striking clues: red fingertips suggestive of a Native American origin, and a chest tattoo depicting the ancient Mayan god Kukulkan. Back at his penthouse, Doc discovers that intruders have destroyed his father’s personal papers, intensifying his resolve to uncover the truth behind the murder.
Vowing to pursue justice, Doc heads south to Hidalgo with the brain trust known as The Fabulous Five, his loyal allies at his side. They soon find themselves entangled with the international criminal and smuggling mastermind Captain Seas, who repeatedly tries to eliminate Doc and his companions. The conflict escalates into a wild and deadly melee aboard Seas’ yacht, the Seven Seas, revealing Seas’ relentlessness and willingness to use any means to stop Doc.
As the investigation unfolds, Doc discovers a historical thread: years earlier, Professor Savage had received a vast land grant in the Hidalgo interior from the Quetzamal, a Mayan tribe that disappeared centuries ago. The trail grows murkier when Don Rubio Gorro, a government land official, explains that the records of the land transaction are missing, raising questions about who truly controls the claim. Mona Flores, Mona Flores, Gorro’s assistant, emerges as a crucial ally who witnessed the original papers and offers to guide Doc and the group to the land claim.
Following the clues left by his father, Doc and his friends uncover a hidden entrance into the Valley of the Vanished, where the Quetzamal still live. In a perilous moment, Doc splits from the group and confronts a pool of molten gold, while learning that Seas is exploiting the Quetzamal as slave labor to extract the precious metal for his own gain. The danger intensifies when Seas’ henchmen capture Mona and the Fabulous Five, and Seas unleashes the Green Death, the airborne plague that previously felled Doc’s father and that keeps the Quetzamal under Seas’ control.
A climactic clash of styles pits Doc against Seas, and Doc emerges victorious, forcing Seas to release his captives. Doc administers a life-saving antidote to the team, and the chase resumes as Seas’ men attempt to flee with the gold. A catastrophic explosion of dynamite triggers the molten gold pool, engulfing the fleeing crew and even Don Rubio Gorro in a fiery baptism of metal.
With Seas brought to heel, Chief Chaac offers the gold and the land grant to Doc, who accepts with a solemn vow: "I promise to continue my father's work ... his ideals. With this limitless wealth at my disposal, I shall be able to devote my life to the cause of justice." The moment marks a turning point, and the story shifts toward a new chapter in Doc’s crusade.
Back in the United States, Doc returns to his private rehabilitation center in Westchester County, New York, where he undertakes acupuncture brain surgery on Seas to reform him rather than simply punish him. As Christmas approaches, Seas appears as a reformed figure—a Salvation Army bandleader—flanked by his former lovers Adriana and Karen, hinting at the complexity of the characters’ fates.
Yet even as Doc savors a moment of peace, a fresh warning arrives. An urgent message, recorded on his answering machine, signals a threat that could cost millions of lives. Undeterred, [Doc Savage] heads toward the next mission, his resolve reaffirmed and his purpose clear: justice, no matter the cost, as he steps back into action for another perilous adventure.
