Fiona Denning, a twenty-five-year-old from Boston, boards the Queen Elizabeth with her two best friends, Viviana "Viv" Occhipinti and Dottie Sousa, to serve as Red Cross Clubmobile girls in wartime Europe. Clubmobile workers drive converted trucks to military camps, serving coffee, doughnuts, and companionship to soldiers. On deck, Fiona spots a blond soldier she mistakes for her fiancé, Second Lieutenant Danny Barker, declared missing in action eight months earlier after his plane was shot down over Germany. She confesses to Viv and Dottie what they have already guessed: Her primary reason for volunteering is to reach Europe and find Danny. Viv, a frustrated advertising secretary, wanted adventure and purpose. Dottie, a shy music teacher, wanted to push herself out of her shell. A chatty former gossip columnist named Blanche Dumond quickly befriends the trio.
During a sleepless night on the ship, Fiona meets Captain Joe Brandon, a swing band leader from Chicago who tells her that seeking answers about Danny is brave, not crazy. He mentions his girlfriend, Mary Jane, waiting at home, a detail Fiona later shares with Dottie, who has developed a quiet crush on Joe.
In London, Judith Chambers, the exacting Red Cross field director, announces that the women will likely be stationed in the English countryside rather than France, crushing Fiona's plans. A V-1 buzz bomb, a pilotless explosive, strikes near Euston Station, introducing them to the dangers of wartime Britain. Fiona bonds with Frankie Cullen, a tough former shoe salesgirl from Chicago whose husband was killed in North Africa, and meets Martha Slattery, a farm girl from Iowa. At Rainbow Corner, the Red Cross club near Piccadilly Circus, the group encounters Harry Westwood, a dashing British RAF officer who briefly chats with Viv before walking away, leaving her intrigued.
Training proves difficult. All three women are poor drivers, and a pressurized doughnut cylinder explodes during practice, covering the kitchen in dough. At a garage, Fiona meets Captain Peter Moretti of the 82nd Airborne Division, a former heavyweight boxer from the Bronx, fresh from Normandy, where his unit lost nearly half its men. He bluntly dismisses the Clubmobile program as unnecessary. Miss Chambers warns Fiona privately that all three must prove themselves to earn a transfer to the Continent.
The crew is assigned to Leicester, billeted with Mrs. Tibbetts, a warm widow. Liz Anderson, their field captain, assigns daily routes, and Fiona is named captain of the Cheyenne. Their civilian driver, Jimmy English, has a drinking problem but proves skilled behind the wheel. Soldiers are overjoyed to see American women, and several become regulars, including Tommy Doyle, a fellow Bostonian. Harry Westwood serves as liaison at a shared RAF base, deepening Viv's fascination with him.
A letter from Danny's mother delivers the first concrete clue: An intercepted German broadcast mentioned Danny's name as a possible prisoner of war, though the report remains unconfirmed. Fiona asks Peter to contact a friend at the International Red Cross (IRC) who tracks POWs but lies, calling Danny a neighbor rather than her fiancé. On a late-night jeep run to deliver coffee to soldiers, Jimmy reveals he lost his wife and daughter in the London Blitz of 1940, explaining his drinking.
Miss Chambers's observation visit becomes a disaster: Dottie slices her arm on a lard tin, a volunteer floods the kitchen, and the doughnut machine makes a mess. The Cheyenne will not join the first group sent to France. Blanche, Martha, and Frankie receive orders to the Continent.
At a secret Glenn Miller concert for departing troops, Dottie takes the stage as a guest vocalist and stuns the audience with "Someone to Watch Over Me," earning a standing ovation and a compliment from Glenn Miller himself. That night, Peter asks Fiona to dance, and afterward, in a park, he asks why she lied about Danny. Fiona admits she has feelings for Peter but pulls away when he leans in to kiss her, torn by guilt.
When the 82nd Airborne ships out for Holland, Peter gives Fiona his Purple Heart. Joe comes to say goodbye to Dottie, presenting a letter breaking up with Mary Jane and declaring his love. Days later, officers' praise, Dottie's debut, and Liz's recommendation convince Miss Chambers to send the Cheyenne to France.
The Continent confronts them with devastation: the wreckage of Utah Beach, demolished villages, and streams of refugees. In Cherbourg, they learn from Patrick Halloran of the 82nd Airborne that Tommy Doyle was killed in Holland. Captain Guy Sherry, an officer Blanche has been flirting with, becomes their military liaison. On their first day in the French countryside, a soldier runs into an uncleared minefield to save wandering children and is killed, a harrowing introduction to front-line realities.
In Paris, Viv discovers that Harry is actually a baron from one of England's wealthiest families. When she confronts him, he admits his family would not accept an American, and Viv, devastated, ends the relationship. Peter takes Fiona to a small café, where they share their first kiss. He then reveals news from his IRC contact: Danny is alive at Stalag Luft IV, a POW camp in East Prussia. Peter tells her he found the information because she deserved to know, even though it meant losing her. Fiona recommits to finding Danny.
In Bastogne, Belgium, a woodstove explosion burns Martha and Frankie. The German Ardennes counteroffensive catches everyone by surprise. Fiona volunteers to deliver Christmas mail to the 106th Infantry Division at Vielsalm, honoring a promise she made to the division's commanding officer, Major General Jones. The front has shifted overnight, trapping the Cheyenne behind enemy lines. For days the women serve soldiers under artillery fire. Major General Jones arranges a narrow escape window.
During the drive out, a jeep crash injures Colonel Brooks, an officer from another division who is escorting them to Allied lines, and the group shelters in a German cottage on Christmas Eve. The homeowner, Elisabeth, admits three lost German soldiers, including Jens, a medical student who tends the colonel's wounds. Over dinner, Americans and Germans share stories through Elisabeth's son Fritz, who translates. Dottie sings carols, and the group shares a fragile evening of peace before departing at dawn.
Back at Allied lines, Peter finds Fiona, having stayed an extra day to search for her. He tells her he loves her, and they kiss before he departs for the front. In Verdun, the women learn Martha was killed when her hospital was bombed. The loss devastates all of them.
In the war's final months, Colonel Brooks arranges for their crew to be among the first Clubmobiles sent to help liberated POWs. At a former Luftwaffe base, a soldier named Chris Sullivan recognizes Fiona from a photograph Danny carried. Chris and Lee Valenti, a fellow POW from Danny's group, tell her Danny was executed by German guards during a forced march from Stalag Luft IV after being deemed too weak to continue. They add that Danny saved many lives through his selflessness. Lee gives Fiona Danny's final letter.
In the letter, Danny asks Fiona to live fully, to fall in love again and honor his memory by embracing life. After recovering from pneumonia on the French Riviera, Fiona reunites with Peter in the fishing village of Villefranche-sur-Mer and tells him she loves him. Peter has been ordered to Berlin for occupation duty, and Fiona applies for a Red Cross position there.
At Viv's wedding to Harry, now reconciled after he declared his love publicly and promised to introduce her to his family, the five remaining friends gather at the Hotel George V in Paris. Blanche is pregnant and marrying Captain Guy. Dottie has been offered a touring soloist position with Glenn Miller's band, an opportunity Miller himself discussed before his plane disappeared over the English Channel. Miss Chambers confirms Bronze Stars for the Cheyenne women. Fiona reflects on how the war destroyed the life she had planned but gave her one shaped by friendship, loss, purpose, and a love she found the courage to embrace.