The US declares war on Germany. Maren Bloch, a clerk at a Milwaukee library branch, suggests a gardening display, because everyone should strive to grow as much of their own food as possible. Her boss decides Maren should give a talk on gardening. Her talk goes so well, she's asked to speak at other places. At the Wisconsin Women's Club, she suggests they compile a wartime cookbook. She's put in charge. When will she learn to keep her ideas to herself?
Peter is drafted and reports to the National Guard. The Guard leaves for training in Texas. Peter excels at training. They move to NJ and boards a former German liner to journey to France. They begin their service as caretakers of the army's horses and mules before being assigned to Alsace. They become the first Americans on German soil. Later, they fight at Chateau Thierry, a horrifying experience. Mitchell Hunsader, the son of Maren's tormentors and a bully, proves to be a coward.
Maren tells her friend how the library's campaign to collect books for soldiers is bringing in books unsuitable to send to the troops. When she is arrested for stealing supplies for the fighting men, she realizes someone was eavesdropping. Her home is broken into by members of the Loyalty Legion. She acquires a poodle to serve as watch dog.
She hasn't been receiving Peter's allotment for a long time. Her next-door neighbor, a lawyer, suspects Mr. Hunsader, Milwaukee's post master, has been stealing her mail. He is arrested and convicted.
Maren and her friend Emily are on a float for a Liberty Loan drive. It depicts gardening and the cookbook. She is exposed to the flu going around the world and becomes ill.
The Nat'l Guard takes part in the battle for Juvigny. Peter is assigned to reconnaissance. His two companions drown in mud. He stumbles into an underground bunker and discovers battle plans. Trying to get them back to their lines, he is wounded. While lying in a Paris hospital with his leg in traction, he is awarded the Medal of Honor. The plans and map he acquired made all the difference in the battle.
Peter finally arrives home. The Blochs try to resume their quiet prewar life, but Peter is famous now. They travel to Washington three years later for the unveiling of the Tomb of the Unknown. They are eager to return home to their young daughter.
