In a North Korean prison camp in 1951, an American soldier is shot by Korean soldiers as he tries to escape. A few years later, in his military law offices on Governor's Island in New York, Col. Bill Edwards is under pressure from his superior, Gen. Connors, to wrap up a seemingly obvious case of treason against the ranking American officer at the prison camp, Maj. Harry Cargill. Bill interviews one of Cargill's soldiers, Lt. George Miller, who recounts that during nine months of starvation and torture, not one man broke under the strain, but then, in rapid succession, two men died and Cargill became a Communist collaborator. Miller recalls the day that Cargill broke: After once again being placed in the hold by ruthless Col. Kim, Cargill returns to his men and begins spouting Communist doctrine, convincing them that he has gone over to the enemy. Miller continues that they were shocked and horrified, especially after learning later that Cargill had signed a confession about the Americans' use of germ warfare and made radio broadcasts supporting Communism. When Bill questions Miller about the deaths of the two soldiers, Lt. Harvey and Capt. Joe Connors, the general's son, Miller states that they died of dysentery, and provides a scientific explanation of the illness. Declaring his confusion at Cargill's treachery, Miller remembers the major reciting at the lieutenant's graveside, "My brother died that I may live." Just then, the general enters and, upon learning that Miller was friendly with Joe, invites him to lunch. After Connors leaves, Bill's aide, Sgt. Baker, chastises his boss for wasting time on the case, which is not only "open and shut" but also has personal significance to the general. After Bill dismisses Baker, Cargill arrives and tersely confesses to all the charges against him, including one Bill knows he did not commit. Bill demands to know why he confessed to something he did not do, and urges the major to help mount his own defense, but Cargill remains silent. Before allowing him to leave, Bill plays Cargill's treasonous radio broadcast, noting the major's building anxiety. After Cargill leaves, Bill works on the case all night, hoping to solve the mystery of why the formerly exemplary officer "broke," and in the morning, Bill's secretary, Cpl. Jean Evans, protects him from Baker's intrusions. Bill then visits Cargill's wife, who lets him in reluctantly but agrees to talk upon realizing that Bill believes in her husband. She reveals that Cargill has not discussed the prison camp with her, and has indeed barely talked to her at all in the time he has been back from Korea. At Bill's questioning, she finally remembers one quote from a letter Cargill wrote her, which she hopes may be useful: "He who kills one man kills a whole world. How many worlds have I killed?" Back in Bill's office, Cargill is waiting for their next appointment. Before letting him in, Bill discusses the case with Jean, fretting over the differences between the traitor depicted in his files and the sensitive soul described by Mrs. Cargill. Jean points out that each witness described dysentery in the exact same words, which suggests that they each memorized a statement to recite. Just then, Gen. Connors returns to rebuke Bill once again for prolonging the case, calling for an immediate court-martial. After Bill politely refuses, Baker verbally attacks the waiting Cargill for putting Bill's job in jeopardy through his refusal to speak. Jean agrees, urging Cargill to tell the truth, but Cargill responds that sometimes the truth can be more vicious than a lie. He tells her that any man's mind will "turn to water" when enough pressure is applied to it, after which he will be called a coward. Bill returns, and although he pushes Cargill to explain why he suddenly became a collaborator after months of resistance, the major remains silent. Later, Bill calls Miller back and, bringing Jean, Baker and Cargill into the office with them, has the boy repeat his testimony about the dysentery deaths. When Miller falters over some of the words, Bill prompts him by reading from the records, proving that Miller is reciting by rote. Realizing he has been caught lying, Miller breaks down, revealing the truth about Connors' death: After Harvey is killed by the guards while trying to escape, the rest of the men discover that Connors tipped off Kim, under torture, that Harvey was planning to escape. The men decide to kill the "stool pigeon," despite Cargill's entreaties not to, and draw straws to choose a murderer. Miller draws the short straw, and despite Connors' screams for mercy, strangles him. Back in the office, Miller weeps that he had no choice, and Bill destroys the record of his confession, instructing him that no charges will be filed against him. Cargill still refuses to explain his own treason, insisting that his story can only hurt the rest of the men who survived Kim's constant torture. As Miller becomes hysterical, the general enters and hears the lieutenant condemn his son, until Bill punches Miller to keep him quiet. Connors, however, insists on knowing the truth about Joe, and when Cargill will not speak, excoriates the major as a liar and coward. Unable to stand by, Bill breaks in and reveals the truth to Connors, who sadly denounces his son. Cargill argues with Connors' assessment, stating that there must be a time limit on being a hero. Joe, he says, was a hero for hundreds of days and a coward for only one, so why must he be judged for that one day? Finally, Cargill reveals his own "cowardice": After Joe's death, Kim told him to capitulate or all his men would be killed, and unable to sacrifice his men, Cargill submitted. More gently, Connors defends the military code of honor, pointing out that every military leader is faced with the responsibility of sacrificing some men for the greater good, and cannot rely on his emotions but only on the code, "our bible." He leaves, calling for Bill to recommend a court-martial, but instead Bill files a recommendation that all changes be dropped. He tells Cargill that this will not save him from a trial, but that he will personally stand as his defense lawyer. As Cargill leaves, relieved that finally at least one person understands his choice, Bill sends his regards to Mrs. Cargill.