In the rugged and mysterious Gobi Desert, a caravan comes to a halt for the night, setting the stage for intrigue and danger. During the night, an attempt is made by an unknown figure to steal a valuable scroll by sneaking into a tent. However, Peter Lorre portraying the cunning adventurer and soldier of fortune Kentaro Moto is secretly awake and swiftly takes action, killing the thief to protect the sacred artifact. As the caravan reaches Peiping, Moto finds himself in trouble when the police search him and uncover the stolen scroll. In a quick display of his cleverness, Moto seizes the scroll and manages to escape, beginning a perilous chase filled with deception and conspiracy.
To lay low, Moto changes out of his disguise and attends a social gathering hosted by Sig Ruman playing the formidable Colonel Tchernov, in honor of the charming Jayne Regan as Eleanor Joyce. During the festivities, Moto discreetly observes a tense exchange: a young noble, Philip Ahn as Prince Chung, leaves his mother to speak privately with Tchernov. It soon becomes clear that Tchernov is interested in acquiring rare family heirloom scrolls, offering a hefty price. When Prince Chung refuses to sell, Tchernov's temper flares, and he pulls out a pistol. However, before he can use it, Moto intervenes, and in a dramatic turn, kills Tchernov — but the deed appears to be a suicide, as Joyce witnesses the scene, making it look like Moto was merely covering up heavy secrets.
Later, the mysterious Prince Chung reveals that the seven scrolls hold the secret of Genghis Khan’s lost tomb and his legendary treasure. One of these scrolls, previously lent to an exhibition, has been stolen, which complicates the quest further. Meanwhile, John Carradine playing Pereira, a dealer in ancient artifacts, introduces Joyce to a fake scroll. She is tempted by an authentic one but finds the price too steep. As she and her associate, Thomas Beck as diplomat Tom Nelson, walk through the city, they notice Moto entering Pereira’s shop. Moto confronts Pereira to reveal he has the real scroll—stolen from the exhibition—but before they can investigate further, Pereira is suddenly shot and killed by an unseen gunman swiftly fleeing the scene.
Moto returns to his apartment, only to find it thoroughly ransacked. He senses an intruder and inadvertently leaves his gun out, which leads to him being held hostage by Wilhelm von Brincken’s character, Schneider, who forces Moto at gunpoint to hand over the scroll. When Moto attempts to escape, Schneider shoots him with what seems to be a gun—only to reveal the weapon was loaded with blanks. Moto, quick on his feet, tracks Schneider to Madame Tchernov, who is played by Nedda Harrigan, and finds her with her lover and the villainous Herr Koerger, portrayed by Sidney Blackmer. As they prepare to rendezvous with their gang, Moto is knocked out by the butler, Ivan, and Joyce is taken hostage.
The mastermind Herr Koerger manipulates the situation, forcing Prince Chung’s mother to reveal the “scrolls’” location through threats. When the prince’s mother attempts to defend her family, she is tragically killed by Koerger. The scene shifts as Nelson finds and revives Moto, and together they rush to save Prince Chung, who has been left behind. But they arrive too late: the prince, after feeling dishonored and betrayed, chooses to end his own life. Moto, devastated but resolute, promises to avenge the prince and protect the cursed tomb from further desecration.
In a daring pursuit, Moto and Nelson follow the criminals aboard a junk, where a tense showdown unfolds. After enduring multiple attempts on his life, Moto exposes Koerger’s false claim to the treasure by revealing that the scroll he sold Schneider is a fake. In a final act of cunning, Moto manipulates the villains by planting discord: he falsely tells Madame Tchernov that Koerger is secretly in love with Joyce, leading her to confirm this untruth. Seizing the opportunity, Moto kills Koerger amidst the chaos. Driven by his commitment to honor the prince’s memory and his vow to safeguard the tomb, Moto then burns the remaining scrolls, destroying the dangerous secrets they hold and ending the saga with a moral victory, even as the treasure remains lost.
