Rose introduces herself using her code name, Dragonfly. The man identifies himself as Lazare. She notices his thumb and forefinger feel rigid. Rose buries her flight suit and helmet while Lazare leads her to retrieve parachute canisters, then signals the reception committee, who arrive with Felix and Muriel. A middle-aged man introduces himself as Claudius, a leader within the French Resistance.

The group carries the supply canisters to a barn in Ableiges to wait until morning. They discover the bicycle intended for Rose has a cracked rim. Lazare argues it is safer to steal one locally than to risk another RAF supply drop, and Felix and Claudius agree. Rose notices Lazare wears a wooden prosthetic hand.

The next morning, Claudius gives them apartment keys and explains they will be smuggled into Paris in a hidden compartment beneath the boards of a lumber truck. He tells them to contact either him or Lazare for Resistance matters, vouching for Lazare’s trustworthiness. They pass through a German checkpoint without detection and separate at a lumberyard on the city’s outskirts, taking different routes to their apartment building. Walking through Paris, Rose is struck by the grim changes under occupation: starving citizens, armed patrols, and swastika flags everywhere. She remembers childhood visits with Charlie and her parents, making the occupied city feel especially heartbreaking and unfamiliar. Two Wehrmacht soldiers stop her to check her papers, and she deflects suspicion by offering to sell them cosmetics. She reaches the fourth-floor apartment, where Felix and Muriel let her in. A knock at the door causes alarm, but it is Lazare, holding a bicycle.

Lazare enters with the stolen bicycle, explaining he has removed its serial number and distressed the paint to make it untraceable. He informs them that Claudius is detained, so he will show Rose the dead drop locations. Felix gives Rose a coded message for Prosper, the leader of the Physician network.

Rose insists on traveling separately to avoid drawing attention. In an alley in Le Marais, Lazare shows her a dead drop for contacting Prosper—a loose brick in a masonry wall—and she successfully plants the message. Walking toward Montparnasse, he points out safe houses for arranging in-person meetings. At Montparnasse Cemetery, they encounter a gravedigger and pretend to be mourners. Lazare shows her a second dead drop hidden behind a plaque on a crypt.

When Rose asks why he does not use a bicycle, Lazare deflects, citing his prosthetic hand. He does not reveal the true reason: Jews are forbidden from riding bicycles. Before parting, he tells her the location of their network’s dead drop—a false wall in a flower box near her apartment. After she leaves, Lazare regrets not being more forthcoming about the antisemitic atrocities and resolves to tell her if they meet again.

On June 1, 1943, Lazare walks to Felix’s automobile repair shop with plastic explosives for a mission to destroy a transformer station near SD headquarters. Felix had recruited Lazare as the best saboteur for the job, with Claudius endorsing him as next in rank to lead the Resistance group.

At the garage, Lazare warns them the rear door is not soundproofed. After some tension, he reveals his real name—Lazare Aron—and his forged identity: Laurent Allard. He again urges them to move Muriel, describing the SD’s wireless detection vehicles. Felix dismisses the immediate danger, then reveals that Rose, not he, will accompany Lazare on the mission.

Rose and Lazare review the sabotage plan. She has already scouted the target and notes a guard who may have a dog. At the transformer station that evening, they cut through the fence, and Rose insists on placing the explosives on the side away from their escape path. After they light the fuses, one fuse Lazare set comes loose, and he must fix it before running. He trips, alerting the guard and his dog. Rose escapes through the fence, but the dog attacks Lazare as he follows, biting his hands. He holds the fence shut to buy Rose time, then jams the wire cutters into it before fleeing.

With sirens approaching, Lazare reaches Felix’s garage, where Rose pulls him inside just as a police car passes. She tends to his bleeding hands with brandy as antiseptic. Lazare tells her she saved his life by placing the explosives correctly and reveals his parents are gone; Rose tells him about her own family’s deaths. A Wehrmacht patrol passes, and they hide in the back of a disabled car for the night. Lazare gives Rose his jacket, and she falls asleep on his shoulder while he keeps watch.

Rose wakes in Lazare’s arms the next morning and reflects that he is unlike any man she has known. Noticing his wounds, she decides to leave sulfa pills for him at his dead drop.

Felix arrives at the garage. Rose and Lazare emerge from hiding. Felix gives Rose a message for Prosper and tells her to alert Muriel about a wireless transmission that evening. Rose again insists on moving Muriel; Felix promises it will be soon. Lazare warns that SD wireless-detection vehicles will eventually locate Muriel if she continues transmitting from the same apartment. Lazare offers to arrange safe houses for Muriel. After he leaves, Felix warns Rose to be careful, implying concern about romantic involvement. She denies anything happened.

Back at the apartment, Rose finds a relieved Muriel and recounts the mission, including that Lazare knows their names. Muriel accepts Rose’s judgment that he is trustworthy. Muriel confesses how much she misses her baby daughter, Mabel, fearing she will be forgotten. Rose comforts her, quietly feeling guilty about the photograph of Mabel that Muriel had been forced to surrender before deployment.

On June 2, 1943, Rose delivers a message to Prosper’s dead drop, then goes to Montparnasse Cemetery to leave sulfa pills for Lazare. On her way home, she observes increased security and witnesses desperate Parisians fighting in a ration line. She is especially horrified by the growing antisemitic persecution throughout Paris and the role French police play in enforcing it.

In Place de la Madeleine, a stylish cabaret singer named Zelie approaches and asks to see Rose’s cosmetics, then invites her to her suite at the Le Cygne Hotel. In the lavish suite, Rose is disgusted by the opulence amid widespread starvation. A Nazi officer Zelie calls Josef enters—Rose identifies his rank as Sturmbannführer and suspects with horror that he may be Hans Josef Kieffer, the head of the SD. Zelie asks to buy the shade of lipstick Rose is wearing, which conceals her suicide pill. Rose lies that she is out of that shade but will get a new tube from her supplier, sells Zelie other items, and quickly leaves.

Three streets from her apartment, Rose spots an SD wireless detection vehicle. She races upstairs and pulls a wire from Muriel’s transmitter just as she is mid-transmission. Felix yanks the antenna inside as the SD car roars past. Felix finally admits Rose was right about the danger and agrees to move Muriel. He also reports that the Germans have already restored power to the SD headquarters, making their sabotage a short-lived victory. Rose recounts her encounter with Zelie and her suspicion about Kieffer.

On June 9, 1943, Lazare visits Rose’s apartment to thank her for the sulfa pills. He reports that Muriel is safe in her new location, though the conditions are poor, and passes on Muriel’s affectionate warning for Rose to stay out of trouble. Rose invites him to stay for coffee.

Rose tells Lazare how she joined the SOE: Her French fluency caught the attention of recruiters while she was working as a war room typist in London, and she secured her place by breaking into an instructor’s office and altering a negative report. She explains she joined to fight the Nazis who killed her parents in a bombing raid and her brother Charlie, an RAF pilot shot down over the English Channel.

As Rose asks about his family, Felix returns to his apartment across the hall. Lazare explains that his parents were pacifists who believed in the power of art and writing rather than violence. Lazare prepares to leave, but Rose insists on accompanying him, so they are on equal terms, since he knows so much about her. He agrees and tells her to wear old clothes because they are going underground.

Lazare leads Rose to a secret manhole entrance to the Paris catacombs near Montparnasse Cemetery. They descend into tunnels decorated with medieval carvings and walls of human bones, navigating by a fading flashlight. He brings her to his personal sanctuary—a small chamber with a cot, blankets, books, and his mother’s painting of the Arc de Triomphe.

He tells her his life story: His parents were Polish Jewish immigrants who built a good life in Paris, his father a journalist and his mother a painter. He had dreamed of becoming a journalist but was barred from the French army due to a hand maimed in a childhood printing press accident. He could not find work at German-controlled newspapers. He became a janitor at Gare du Nord and began posting anti-Nazi propaganda alone, then turned to sabotage after witnessing a German officer shoot a man for reading one of his posters. Claudius saved him from Wehrmacht officers and recruited him into the Resistance.

Lazare reveals that his parents were arrested by French police during the Vél’ d’Hiv roundup and deported in cattle cars. He fears he will never see them again. Rose comforts him. She offers him the spare room in her apartment, but he refuses. As they leave, his flashlight dies and he leads her by the hand through the darkness. At the base of the ladder to the surface, Rose hugs him and kisses his cheek. He helps her up, then returns to the catacombs alone.

Two weeks later, Rose persuades a reluctant Felix to let her accompany him to visit Muriel at her new safe house. She is upset by the poor conditions and defends Lazare against Felix’s criticism. London replies to Muriel’s transmission, stating that the next supply drop—which is supposed to include a replacement lipstick for Zelie—is postponed two weeks. Felix decides they cannot wait and, using a heated knife, skillfully alters Rose’s own suicide pill lipstick to look new and swaps it into a fresh tube. After Felix leaves, Muriel mentions that Lazare was asking about Rose.

Rose goes to Le Cygne Hotel. Zelie lets her in while Kieffer is in the shower. While Zelie searches for her purse, Rose examines papers on Kieffer’s desk and sees the cover of a report titled in German, Gedeihen/Arzt. Lifting the page, she glimpses a list of what appear to be non-German names before Kieffer emerges from the bathroom. Rose gives Zelie the lipstick, takes payment, and leaves under Kieffer’s hostile stare.

Shaken and fearful the list indicates an infiltration of SOE networks, Rose rides to Montparnasse Cemetery and leaves a note for Lazare requesting to see him.

Rose rushes to Felix’s apartment and tells him she fears the Physician network has been infiltrated, based on the report she glimpsed. A name on the list that may have been Frank. Felix is highly skeptical but agrees to have Muriel make an unscheduled, high-risk wireless transmission. Headquarters reports that all wireless operators are accounted for and believes the networks are secure. Rose remains unsettled, wondering if the SD could have captured an operator and obtained their security codes.

Late that night, Lazare arrives, having received her message. Rose tells him everything, admitting her concerns are largely based on intuition. Lazare affirms his trust in her and decides to suspend all dead-drop use and establish new safe houses as a precaution. He creates a new way for her to contact him—slipping notes into the manhole cover of his secret catacomb entrance.

Seeing she has not eaten, Lazare cooks a meal from scraps and they share apple brandy, talking about their pasts, their lost families, and their dreams for after the war. Rose asks him to stay the night, as it is past curfew. They kiss and go to her bedroom, where they make love.

On the morning of June 23, 1943, Lazare rises early to meet with Claudius. Rose awakens, and they share a tender moment before he leaves, promising to return that evening. As he walks, Lazare reflects on his deep feelings for Rose and the hope she has given him, but he worries their relationship could force them to choose between love and duty.

He finds Claudius alone in a basement safe house and relays Rose’s concerns about a possible SD infiltration. Claudius agrees with Lazare’s plan to suspend dead drops and find new safe houses, and Lazare shares the location of his secret catacomb entrance with him for secure communication.

Claudius then reveals that the Physician network has requested a reception committee for that night to meet a new agent arriving by RAF Lysander. Claudius intends for both of them to go, but Lazare argues it is too risky for the two leaders to be on a mission together. Unwilling to let Claudius take the risk alone, Lazare proposes they flip a coin to decide who will lead the committee. Claudius agrees. As Lazare flips the coin, he realizes the outcome will determine whether he gets to see Rose again that night.