Upon the United States entry into World War I, the first American units to arrive at the front in France are veteran Marine Company (military unit), one of which is commanded by Captain (United States) Flagg, along with his lieutenants, Moore and Aldrich. Flagg has developed a romantic relationship with the daughter of the local innkeeper, Charmaine, and resumes their relationship after returning from the front. However, he lies to her and tells her he is married when she wants to come with him on his leave to Paris. Replacements arrive and their lack of discipline and knowledge infuriate the captain. But he is expecting the arrival of a new top sergeant, who he hopes will be able to train them properly. However, when the sergeant arrives, it is Quirt, Captain Flagg's longtime rival, and their rivalry quickly re-ignites.