Wealthy Elmer J. Stuyvesant is continually thwarted in his efforts to court Mary, a local shop girl. Mary wants nothing to do with his invitations for "a little dinner and a show," until Elmer gets swept up in the hubbub of World War I and is accidentally inducted into the army, mistaking a recruitment office for an employment service. When told to strip for his physical examination, a shocked Elmer protests that he really didn't need a new chauffeur after all. At boot camp, Elmer is among a motley bunch of bumbling recruits who are ordered around by the exasperated Sergeant Brophy, of K Company, who attempts to show them the fine art of stabbing the enemy with a bayonet and marching in a straight line. Elmer wants to resign from the army, but changes his mind when he meets up with Mary, who has joined the entertainment division.
Elmer visits Mary with a bag of gumdrops and wins her affections, but he is unaware that Sergeant Brophy also has eyes for her. That evening, as all leave passes are revoked, they each sneak out to see her before the troop ship sails for France. The two men show up at Mary's house, and she denies knowing Elmer, in an effort to save him from Brophy's bad temper. Perplexed, Elmer dons a military police arm band and tricks Brophy by chasing him all the way back to the barracks.
Sailing to France, Elmer, Guggleheimer, and Nescopeck entertain their fellow travelers with some scat singing and ukulele strumming. When an emergency drill catches Elmer in the shower, he arrives on deck wearing only a towel. Spotting Mary on an upper deck, he crawls under a canvas tarp to hide, only to run for cover when she discovers him. In rainy France, Mary explains everything to Elmer while he is on sentry duty. His gun goes off for no apparent reason, and he is arrested and ordered back to his barrack. Dazed with thoughts of love, Elmer falls out the barrack's window and stumbles into a French girl's bedroom, where her father finds him the next morning. Mary witnesses the spectacle of Elmer, proclaiming his innocence, being marched to the Sergeant's tent by the French father and his daughter.
Nescopeck urges Elmer to join K Company's show, in order to get back into Mary's good graces. At the evening performance, Elmer parades on stage with the other chorus line "lovelies," only to be chosen as the female partner in a brutal apache dance. Elmer's punishment abruptly ends when bombs are dropped on the makeshift theatre, and the squad scrambles for battle.
Now in the trenches, Elmer volunteers to go into No Man's Land and return with a German prisoner. Under the cover of darkness, Elmer drags back a prisoner, only to see that it's a scared and confused Nescopeck. Elmer tries again, landing in a German foxhole and catching the enemy off guard. He meets up with his former valet Gustave, who explains that he and his men are starving and weak. Elmer vows to return with food in exchange for a luger, which happens to be wrapped in the enemy's attack plans. The war ends before Elmer has the chance to reciprocate the favor, whereupon Gustave immediately asks for his old job back.
Post war, Elmer is married to Mary and has gone into business with his former army buddies manufacturing Gold Medal Ukuleles. When a worker outside the company window sets off a riveter, everyone ducks for cover, including former Sergeant Brophy, now the janitor, who has a flashback and immediately puts the blame on Elmer. — Janice Agnello