John Hathaway [Gregory Peck] is a Nobel Prize–winning university professor turned Western agent, tasked with a high-stakes mission to Communist China: retrieve an enzyme that could let crops grow in any climate. The assignment comes at the urging of Lt. General Shelby [Arthur Hill] at the U.S. embassy in London, and is pressed on him by a direct call from the President. Hathaway is also buoyed by concern from a close friend back in London, Kay Hanna [Anne Heywood], who frets about the danger he faces. A hidden twist shadows the mission: a transmitter is implanted in Hathaway’s skull to track him, but unknown to him, the device also contains an explosive that the United States could trigger if he fails.
As Hathaway lands in Hong Kong, the hunt for the enzyme quickly entwines with political intrigue, because neither the U.S. nor the Soviet Union wants the discovery to remain in Chinese hands alone. In a nightclub, Ting Ling [Zienia Merton] escorts him to Security Chief Yin [Ric Young], where a riddle of loyalties begins to unfold. Back at his hotel, Ting Ling reappears, nudging Hathaway to seduce her as part of a larger chess game; a single phone call interruption leaves him unconscious, and Yin’s men carry him away toward a meeting with the enigmatic Chairman [Conrad Yama]. A tense table-tennis exchange with the Chairman reveals a paradox: while the Chairman speaks of sharing the enzyme with the world, Shelby actively weighs using Hathaway’s explosive collar to eliminate the threat.
Hathaway is then whisked away to reunite with Soong Li [Keye Luke], a renowned scientist, and he also meets Soong Chu [Francesca Tu], Li’s daughter, whose presence further muddies the loyalties of everyone involved. Soong Li, perhaps betrayed, is attacked by guards who seek the coveted formula; before the professor dies, he entrusts Hathaway with a book containing quotations from the Chairman and a fragment of microfilm. Soong Li flees with both the book and the microfilm, making a heroic but desperate dash toward the Soviet border. Shelby, facing a crisis of conscience and the clock, makes the fateful choice to detonate Hathaway’s embedded explosive—but in a dramatic turn, Soviet border troops arrive just in time to escort Hathaway across to safety.
Safe at last, Hathaway discovers that the enzyme’s formula is concealed within the Chairman’s own book of quotations. The threat is confirmed when the device is removed, revealing it could have been detonated remotely at any moment. The revelation is a stark reminder of how close Hathaway came to a catastrophic end, and the mission’s true outcome settles into a quiet hope: the knowledge is preserved, the danger contained, and Hathaway returns to Kay in London, carrying with him not just a breakthrough but also a renewed sense of what it means to be protected by and depend on a fragile web of international diplomacy.
