In 1938, Brad Craig, Richard Quine, the son of a famous Army colonel, begins his freshman year at the Agricultural & Mechanical College of Texas (now Texas A&M University). After spending the past four years in the Philippines, he has acquired an intimate knowledge of Japanese culture and a keen desire to invest in the modernization of Asia. At the train station, Brad is met by cadet Cyanide Jenkins, Noah Beery Jr., his new roommate, and he is introduced to sophomore Panhandle Mitchell, Robert Mitchum, a tough upperclassman who wastes little time in disciplining Brad for various cadet violations. As Brad adjusts to life on campus, he becomes romantically involved with Nina Lambert, Anne Gwynne, the daughter of beloved chemistry professor Pop Lambert, Harry Davenport.
Following an artillery exercise, Brad notices that the brakes on his section's caisson appear to be damaged. Panhandle disregards Brad's concerns and orders the section to move out. When the brakes fail and the caisson careens out of control, Brad risks his life to improvise a solution and prevent a disaster. His quick thinking saves Cyanide's life and earns him Panhandle's respect. Brad is soon promoted to “fish sergeant”, and his upperclassmen delight in exhausting him (smoking him out) by constantly staging fights and ordering Brad to intervene; he finally discovers the game and exacts his revenge.
As Brad's college career progresses, he discusses marriage with Nina, who is secretly smitten with Cyanide (and he with her), though each is hesitant to disclose their feelings. During the Field Artillery Ball, Brad encourages Cyanide and Nina to dance together when they finally admit their mutual attraction. By the following year, they have become a couple with Brad's blessing. Meanwhile, Brad finds himself in a difficult position when his classmates are concerned about his support of Japan. Two Japanese-American cadets, Kubo, Allen Jung and Matsui, Roland Got, come to his aid, their justification of Japanese war crimes angering the others and earning Brad the contempt of his friends.
While guarding the Chemistry Building one night, Brad discusses with Pop Lambert his invention that would protect servicemen from poison gas. Pop hides the formula in his office to prevent tampering, but after he departs, Brad is drugged and locked in a closet, yet he manages to escape, seeing Kubo and Matsui ransacking the professor's office. He trails the pair and confronts their employer, a traveling salesman, William Frawley working for the Japanese. Having taken some papers from Pop Lambert's office, Brad offers to provide the formula in exchange for a bribe, but deliberately gives them a version missing a key element whose absence will render it useless.
Brad is accused of treason for his actions, although the commandant does not have enough evidence to bring formal charges. Ostracized by the student body, Brad decides to leave the university. Months later, Brad is working for the Japanese Navy recording English-language propaganda for distribution in the United States. He is assigned to give radio commentary on an impending Japanese assault on the Solomon Islands. The maneuver is detected and a U.S. Navy carrier group moves to intercept the Japanese fleet.
While airborne to cover the battle, Brad manages to contact the U.S. fighter group, led by Cyanide, revealing his covert infiltration of the Japanese military and offering his services to the American forces. He crashes his own aircraft into the Japanese aircraft carrier, disabling the flight deck and giving the Americans the advantage. Brad dies as the carrier is destroyed and is posthumously awarded the Medal of Honor.
