The novel opens with a frame narrator named Lily, who announces that Blanche Auzello is dead. Lily recalls Blanche as vibrant and courageous, but the most vivid memory is of Blanche at the Hôtel Ritz in Paris, the setting that suited her best. Lily recounts the story Blanche told her of the day in June 1940 when Nazi soldiers stormed through the Ritz's front doors, their swastikas defiling the opulent interiors of the hotel that César Ritz had founded in 1898.
Blanche, an American woman, and her husband Claude Auzello, the Ritz's director, arrive in Nazi-occupied Paris after traveling from Nîmes, where Claude had been garrisoned during the Phony War, the early, uneventful phase of the war. The city is eerily silent, with a swastika flag hanging over the Ritz entrance. Claude looks uncertain for the first time, but Blanche summons her courage and announces them to the soldiers in fluent German, a skill Claude did not know she possessed. A German officer explains that management has been relocated to the rue Cambon side while the Germans occupy the Place Vendôme entrance. In their suite, Claude reveals he smuggled stolen travel passes from his garrison. Blanche is hurt he kept this secret, recognizing he is still lying to her.
In a flashback to 1923, Claude, then assistant manager at the Hôtel Claridge, meets Blanche Ross, a young American accompanying Pearl White, a fading film star. Claude spends a week showing Blanche Paris and falls deeply in love. When an Egyptian prince named J'Ali Ledene arrives to take Blanche to Egypt, she forces J'Ali to admit he will never marry her and chooses Claude, who has proposed. That same day, Claude is offered the position of manager at the Ritz.
Their marriage proves volatile. On the honeymoon train, Claude demands Blanche change her habits; she refuses, and the argument escalates until she escapes at a station before they eventually reconcile. Blanche makes herself an asset at the Ritz, befriending wealthy guests and bringing new business, earning the nickname "Mistress of the Ritz" from an exasperated Claude. Yet their relationship fractures when Claude announces he will spend Thursday nights with a mistress, presenting this as a normal French arrangement. Blanche is devastated, and a cycle of infidelity, flight, and reconciliation defines their marriage for years.
In a flashback to 1937, Blanche meets Lily Kharmanyoff, a tiny, mysterious woman of indeterminate nationality, on a Mediterranean steamer. Lily challenges Blanche to find a cause worth fighting for, tells her war is coming to France, and departs to fight for the Loyalists, the anti-fascist Republican side in the Spanish Civil War. By 1938, the Ritz is increasingly frequented by Germans, including Baron Hans Günther von Dincklage, nicknamed "Spatzy," a member of the Abwehr (the German military intelligence organization). Claude catches Spatzy inventorying the wine cellar and recognizes the Germans are preparing to invade. He tells Blanche he is ending his affairs: There is only time for love and survival.
Back in the Occupation present, Claude insists the Germans present ration books before being served, establishing them as guests rather than occupiers. Frank Meier, the Ritz's head bartender, runs the bar while quietly passing messages for the Resistance. When the phone in their suite rings once at night, Claude leaps up and leaves. Blanche believes he has resumed his affairs.
In autumn 1941, Blanche is beckoned into a shop where a downed British airman has been hiding. She disguises him as a convalescing German soldier and herself as his nurse, walks him through occupied streets, and delivers him to a Resistance contact point. She returns exhilarated but realizes she can hide her activities behind Claude's low opinion of her. Claude, meanwhile, has his own secret: A young man named Martin—a stranger who organizes hotel directors to pass intelligence to the Allies—has recruited him into an organized Resistance network. Claude's nighttime calls summon him to clandestine meetings, not to a mistress, but he allows Blanche to believe he is unfaithful, viewing her ignorance as protection.
In autumn 1942, Lily returns to Paris and reveals that Robert, her lover, was killed by the Nazis. She takes Blanche to meet her Resistance group, and Blanche insists on full participation. She begins delivering microfilm, escorting downed airmen, and driving lorries of hidden weapons. She and Lily return to the Ritz each time appearing drunk, maintaining their cover. The horror deepens when French police round up over 10,000 Jews in the Vél d'Hiv roundup, named for the Vélodrome d'Hiver where victims were confined before transport to camps. When the Auzellos first see yellow Stars of David forced upon Jewish residents, they crawl into bed fully clothed, stricken.
In spring 1944, Resistance members kidnap Coco Chanel, the fashion designer who lives at the Ritz, from her suite for her relationship with Spatzy. Von Dincklage orders a room-by-room search just as Blanche has secretly checked Lily and her wounded lover Lorenzo into a room. Claude discovers them and reveals he too is part of the Resistance. During the search, Lily distracts the soldiers with a theatrical display, and the couple goes undetected.
After the Allied landing at Normandy, Blanche takes Lily to Maxim's, a celebrated Parisian restaurant, to celebrate. Drunk and bold, she toasts the Americans and flings champagne into a German soldier's face. The women flee, and back at the Ritz, the argument that follows becomes a mutual confession: Claude reveals he has been passing intelligence to the Allies and hiding people, while Blanche reveals her own missions. They have been fighting the same fight and tearing each other apart. The conversation reaches their deepest secret: Blanche reveals she is Jewish, born Blanche Rubenstein. She changed her passport years earlier, converting nominally to Catholicism for Claude's career at the Ritz, which enforced unspoken quotas against Jews. Claude gave her a gold cross she has worn ever since. That night, Claude retrieves his gun and contemplates whether he could shoot Blanche to spare her from torture. He cannot.
The next morning, the Gestapo arrests Blanche. At Fresnes prison, she spots Lily among the prisoners and cries out her name, inadvertently identifying a known Resistance member. Lily is hauled away, but her last look at Blanche is one of gratitude. Over months of interrogation, the Germans demand Blanche confirm that Lily is Jewish. She refuses despite starvation, assault, and a dislocated shoulder. When they threaten Claude, she screams that she herself is the Jew, but the Germans laugh, refusing to believe a Jew could live at the Ritz.
On August 24, 1944, as Blanche is about to be executed, the Americans arrive and the guards flee. She glimpses a flash of blue she believes is Lily escaping. Claude finds her collapsed near the prison, skeletal and gray-haired, and drives her back to the Ritz, where she insists on entering through the front door.
The next day, American writer Ernest Hemingway arrives to declare the Ritz liberated. Blanche eventually joins the celebrations but is disconnected, shaking uncontrollably. She undertakes work with Jewish orphans who were hidden during the war and baptized as Catholics, fighting to reconnect them with surviving Jewish relatives. She tells Claude she believes Lily is dead and that she is responsible. She refuses to leave the Ritz, the only place Lily would know to look.
In the closing frame, Lily reveals she survived and watched from afar as the Auzellos grew old together. But Blanche deteriorates, screaming in German, unable to bear light. When Claude retires unwillingly from the Ritz, the couple walks out together. On May 29, 1969, a neighbor hears what sounds like a tire popping, then a second sound three hours later. The maid finds Blanche dead from a gunshot wound and Claude on the floor beside her, gun in hand. Lily speculates it was a mercy killing born of love, suggesting Blanche may have known and lay still, because she was always so good at saving. Lily leaves the question to the reader.