In 1944, before being sent overseas to war, U.S. Marines Nico Kantaylis, Frankie O'Neill and Alan Newcombe return to San Francisco to visit their loved ones. Frankie detests his loathsome stepfather, Charlie Scanlon, and so stops at a local tavern before going home. Alan's father, Amory Newcombe, a man of wealth and social stature, disagrees with his son's decision to enlist, but Alan, an idealistic intellectual, believes it is his moral duty to fight. Nico, a career sergeant in the Marines, visits his pregnant sweetheart, Andrea Lenaine, and insists that they immediately marry. While Nico proposes, Frankie drunkenly stumbles out of the bar and thus fortified, goes home, where he is welcomed by his mother and younger siblings. When Charlie accuses Frankie of being a coward and likens him to his late father, Frankie lashes out and Charlie throws him out of the house. After an altercation with his father, Alan goes to see his socialite fiancée, Sue Trumbell, and finds her drunkenly frolicking with a man named Derek. When Alan discovers Derek's clothes hanging in Sue's closet, he reproaches her and she defends herself by blaming her woes on her mother, an international beauty with a taste for exotic men, who deserted Sue in childhood. On the eve before they are to report for duty, the three Marines, trying to hold back the day, converge at a plush hotel. When Nico and Andrea, now married, are unable to obtain a room in the over-booked hotel, Alan gives them the key to the suite Frankie has reserved to romance his childhood sweetheart Lorraine. At the hotel bar, Lorraine surprises Frankie when she appears in her new WAVE uniform. After Lorraine introduces her exotic roommate, Kalai Ducanne, to Alan, the delicate Kalai, a nurse at the local hospital, tells Alan about her Hawaiian-French ancestry and her desire to better herself by attending night school. As Alan and Kalai talk, Frankie becomes progressively drunker and mauls Lorraine, who has little tolerance for his irresponsible attitude toward life. They all adjourn to Lorraine's apartment, where Frankie pledges his undying love to Lorraine and then passes out on her bed. After Alan and Kalai share an embrace, Kalai confides that she has fallen in love with him, but he protests that they hardly know each other. Their discussion is interrupted by Frankie's drunken screams of terror at the prospect of going to war. After Frankie tries to run away, Lorraine declares that she has lost all respect for him and ends their relationship. Andrea, upon awakening in their hotel suite the next morning, begs Nico to run away with her and their unborn child, but he feels a moral imperative to accompany his men into battle. Later, the three Marines reunite aboard a troopship bound for Japan. When they land on the beach in a hail of gunfire, Frankie cowers in the sand and stays behind. Nico, surveying the bodies of dead soldiers while searching for the missing Frankie, finds him and slaps him into submission. In the following weeks, as casualties mount, Nico begins to doubt the wisdom of war. In San Francisco, meanwhile, Andrea gives birth to a son and Sue is momentarily sobered by the news about Marine losses in Japan. When Danny Krieger, a wise-cracking Marine, is shot by snipers, Alan calls for help, but the cowardly Frankie refuses to come to their aid. Shaken by Danny's death, Frankie is finally inspired to heroism. When, back in San Francisco, Charlie begins to belittle Frankie, his mother and siblings proudly produce a commendation of honor and medal awarded to Frankie. Sickened by the atrocities of war and an attack of fever, Alan begins to question his commitment to the military. In San Francisco, meanwhile, Kalai learns that Sue has been committed to the hospital for attempted suicide and rushes to her bedside. There, Sue, deranged, mistakes Kalai for her errant mother and begins to rant. Alan, now recovered from his fever, decides to reconcile with his father just as Kalai visits Mr. Newcombe to ask for Alan's address. At first suspicious of her motives, Mr. Newcombe is won over by Kalai's sincerity. On the battlefield, Nico is killed while single-handedly trying to stop an attacking tank, and Frankie somberly retrieves his friend's possessions. At the end of their tour of duty, Alan returns home to Kalai, and Frankie, newly promoted to sergeant, visits Andrea to deliver her husband's final letter. Sensing that Frankie also suffers from Nico's loss, Andrea assures him that Nico lives on in their son. Frankie then asks if he can come and see them again, and Andrea gives her assent.