The novel alternates between two timelines, one set during the German occupation of Paris in World War II and the other in present-day 2017, weaving together the stories of two women whose wartime courage is gradually uncovered decades later.
In June 2017, Aurelia "Lia" Leclaire, a French chemical engineer, inherits a Paris apartment from her recently deceased grandmother, Estelle Allard. Lia had no idea the apartment existed. Inside, she finds fine art and a striking nude painting alongside copies of
Signal, a Nazi propaganda magazine, and a postcard inscribed with thanks from Hermann Göring, the head of the Luftwaffe, Nazi Germany's air force. Lia concludes her grandmother was a Nazi collaborator. Among the items Estelle left her is a small painting of a manor house signed by "William Seymour." Lia contacts Gabriel Seymour, a London-based art appraiser, who recognizes the manor as Millbrook Hall, his family's Norfolk estate, painted by his grandfather William. He suspects the nude may be a work by the Norwegian Expressionist Edvard Munch and travels to Paris.
At the apartment, Gabriel confirms the nude appears genuine and discovers a false panel in the dressing room concealing dozens of unframed Impressionist and Expressionist paintings. He then finds that the bedroom wardrobe opens into a hidden room containing a bed, children's books, a sketchbook with the name "Aviva," and a locked trunk holding forged identity papers, a broken violin, concealed weapons, and photos. Lia realizes Estelle was not a collaborator but was hiding people during the war; the Nazi propaganda was a deliberate disguise. The photos depict a striking blond woman identified on a French rail pass as "Sophie Beaufort," dated 1943. Gabriel is stunned: The woman is his great-aunt Sophie Seymour, a brilliant linguist presumed dead in Warsaw in 1939. They travel to Millbrook, where Gabriel's ninety-eight-year-old grandfather William becomes emotional upon seeing Sophie's photos and confirms the family believed she died in 1939. In the estate's attic, they find a sealed, undelivered letter from Sophie to William.
The wartime chapters reveal how these events unfolded. In August 1939, Sophie marries Piotr Kowalski, a Polish cavalry officer, in the town of Wieluń. The next morning, German bombers attack. Piotr shields Sophie and is fatally shot, telling her to make every day count. Sophie spends thirteen months escaping Poland, only to learn that her parents have been killed in the Blitz and her twin brother William, an RAF pilot, is missing. She takes a position at Bletchley Park, the British code-breaking center, under her married name. In 1942, she is recruited for the Special Operations Executive (SOE), the British agency conducting espionage in occupied Europe. Her mission: travel to Paris posing as the wife of a cosmetics businessman to photograph a Tunny cipher machine, a sophisticated Nazi encryption device believed hidden in the Ritz Hotel near Göring's Imperial Suite, and copy its codebooks.
Estelle's story begins in June 1940 as she drives ambulances on the collapsing French front lines alongside her closest friend, Rachel Wyler. Hours after Rachel's brother Alain dies in the fighting, France surrenders. By September 1940, Estelle has returned to occupied Paris, where she infiltrates the Ritz, now Luftwaffe headquarters. She sings for the officers, collects intelligence, and passes it to the Resistance through Vivienne, a courier and cousin of Jerome de Colbert, the field medic Estelle worked alongside during the fighting. During one visit, Estelle discovers a hidden staircase leading to a cellar communications room.
In July 1942, French police conduct the Vél' d'Hiv' Roundup, a mass arrest of Jewish families in Paris. Rachel shoves her five-year-old niece Aviva into Estelle's arms. Rachel, her father Serge, a Jewish doctor who had treated an injured Allied airman in Estelle's apartment, and Aviva's mother Hannah are taken away. Estelle conceals Aviva behind the wardrobe wall, where the child stops speaking. A year later, Estelle hangs three Degas paintings from the Wyler family in the hidden room to comfort Aviva and gives her one of two matching enameled pendants, fastening the second around her own neck, where it will remain until it passes to Lia after Estelle's death.
When Sophie parachutes into France in August 1943, her assigned partner dies during the drop. She connects with the Resistance and meets Estelle at Sacré-Coeur. Almost immediately, Jerome is arrested by the Gestapo while guiding an American airman, and Sophie improvises to save the airman from a suspicious Gestapo sergeant named Schwarz. The two women form a partnership: Sophie arranges for Aviva to be smuggled into Switzerland using forged papers, and after a wrenching goodbye, Estelle agrees to help Sophie infiltrate the Ritz.
They arrive with a wrapped painting presented as a gift for Göring. Estelle charms the guards while Sophie descends through a hidden closet into the cellar, photographs the Tunny machine and its codebooks, and returns in under fifteen minutes. Schwarz and an aide named Hesse have arrived. When Hesse attacks, Sophie kills him with a concealed knife, then stages a hostage scene with Estelle before bolting and drawing all pursuers. Estelle retrieves the film canisters Sophie left hidden behind the painting, flees Paris, and delivers the intelligence to Miss Vera Atkins, Sophie's SOE handler, in London.
Sophie is captured and tortured for days, revealing nothing. In her final moments, she hallucinates Piotr. He asks if she made it count. She whispers yes and reaches for his outstretched hand.
After the war, Estelle visits Millbrook and finds William alive but devastated, missing a leg and dependent on morphine after years in a POW camp. She tells him his sister was brave and never stopped believing he would come home. She buys one of his unsold paintings and returns to France, having learned that Jerome's name appears on a prison escape list but not the recaptured list.
Back in 2017, Gabriel reads Sophie's letter, in which she writes about her marriage and urges William to make every day count. The words speak to Gabriel, who has been hiding his own paintings, afraid to exhibit them. At the Paris exhibit Lia organizes for the recovered collection, she has secretly hung Gabriel's two paintings,
Après and
First Love, with cards reading "ARTIST UNKNOWN." His friend Olivia Allen, the ballet dancer he painted, urges him to be brave. Gabriel replaces the cards with ones bearing his name.
That evening, Dr. Alina Adler approaches with her son Luca, who has noticed Lia's enameled pendant, identical to his mother's. Alina reveals she is Aviva, the child Estelle hid during the war. Adopted by a Swiss family, she became both a doctor and a dancer, just as Sophie once promised. She confirms the Degas paintings belonged to her family and asks that they remain exhibited rather than hidden again.
In the empty gallery after closing, Lia tells Gabriel she has turned down her job in Seville. Gabriel presents her with a restored Collin-Mézin violin from the Millbrook attic, saying he is tired of hiding things. He asks Lia to dance, echoing the anonymous couple in
Après. She takes his hand and says yes.