In 1945, after the official end of World War II, many Japanese soldiers remained interned at a prisoner of war camp on the fictional G Island. Lieutenant Tsubaki, a proud Japanese officer, breaks into the American military infirmary to steal medicine for Corporal Mikami, one of his men who is suffering from malaria. Tsubaki is caught and brought before Major Howard, the American officer in command of the camp. Major Howard offers Tsubaki the medicine in exchange for making Tsubaki his personal plaything. With no other way to save his subordinate, Tsubaki agrees and submits to the major's cruel and degrading games.

The story follows Tsubaki as he returns to Howard, now swearing unconditional submission to become the major’s slave in order to protect his fellow prisoners. Despite his willingness to sacrifice his body, Tsubaki struggles to completely shed his pride as a man and as a soldier. To break him completely, Howard, often accompanied by Sergeant Scott, escalates his torments. Tsubaki is subjected to extreme humiliations including being forced to drink urine, wear soiled clothing, displayed naked in the camp, whipped, treated like an animal, and gang-raped. Over time, the relentless misery causes Tsubaki to slowly develop masochistic desires.

As the cycle of abuse continues, the emotional entanglements among the characters deepen and curdle. Major Howard finds himself unable to control his obsession with Tsubaki, driven by a deranged and destructive love. Sergeant Scott participates in and witnesses the entire affair. Back in the Japanese prisoner barracks, Corporal Mikami remains innocently devoted to Lieutenant Tsubaki, worried for his health without understanding the true price being paid. Sergeant Sakakibara learns the truth about Tsubaki's ordeal but feels helpless to act, trapped by his own powerlessness. Private Sonezaki suffers in the space between his respect for and disappointment in his lieutenant, torn by love and hatred. Their feelings become intertwined and crossed, setting the stage for an unstoppable tragedy.

A critical incident occurs when Major Howard discovers that Tsubaki had previously been used as a plaything by other prisoners. Howard tortures Tsubaki to force him to reveal their names, but the lieutenant refuses to betray his fellow soldiers, enduring the pain to keep them out of jeopardy. The major’s torments grow even more severe and cruel in an attempt to finally break the lieutenant's will, eventually leading to a tragic conclusion on the island.