In October 1917, 23-year-old Nora Crowell, a Nursing Sister with the Canadian Army Medical Corps, tends wounded soldiers at Camp Hill Hospital in Halifax. She cares for Private Doucette, an Acadian soldier longing to return to Chéticamp, and for Sergeant Hammond, who has lost both legs and an eye and recoils from her touch. The despair she witnesses weighs upon her, but fellow nurse Jessie Smiley lifts her spirits. Nora is dating a soldier named Alton “Alley” Vienot. While she enjoys their time together, she has no interest in marriage.

A month earlier, she met Alley when he returned her hat, which had been blown away by the wind. After that first encounter, they met for tea, walks in Point Pleasant Park, and dances. Nora’s older sister, Jane, disapproves of Alley, and Nora wonders if this is partly because Jane is lonely since her husband, Jimmy, is at the front. On one of Nora’s days off, Alley admits he will be leaving Canada to fight overseas soon. He derides the Halifax garrison as “Safety First” boys for staying in Canada. Nora, who has seen the physical and psychological damage caused by the war, is afraid for him. They dine at The Green Lantern and then join friends at a church hall dance, where Nora sips bootleg liquor for the first time. During a waltz, desire flares between them. Outside, their kisses turn urgent, then tender. Alley asks her to go somewhere private, saying he needs the memory of their intimacy to sustain him during the trials ahead. Nora, who questions why women’s sexual desire is stigmatized when men’s is not, chooses to go with him to the Queen Hotel, where they have sex.

Later that night, Nora returns to Jane’s boarding house on Henry Street and discovers that her sister waited up for her because she was worried. Nora says she and Alley went to a dance but doesn’t mention the hotel because she feels somewhat guilty. Jane guesses Nora is in love. Nora admits she cares for Alley but does not know if it is love. Jane worries Nora is changing, becoming careless and losing her independence. Nora bristles and explains that the difficulties of her hospital work make her need Alley’s levity. Hurt, Jane reminds her that she understands the strain of living in wartime because Jimmy is at the front. Nora apologizes, and they reconcile.

Jane recalls how Nora has always had a deep sense of responsibility, citing how the seven-year-old Nora tended their two-year-old brother Willie so their mother could rest after their younger brother Stephen’s birth. Before they part for the night, Jane asks if Nora is all right, noting she looks different. Nora says she is only upset about Alley’s departure. Alone, she wrestles with her feelings and resolves to focus on her duties and put the night with Alley behind her.

On December 5, 1917, Nora dresses for her shift at Camp Hill Hospital. She has missed two periods and feels nauseated and exhausted, so she’s certain she is pregnant from her night with Alley. Though she has written to him weekly since October, he has not replied. Now she checks the casualty boards daily, afraid that she’ll see his name among the lists of wounded and dead soldiers.

In the kitchen, she helps Jane prepare breakfast for Jane’s daughters, Evelyn and Clara, and the three boarders, John, Milton, and Harry. After the men leave, Jane confronts Nora, saying she knows Nora is pregnant. Nora admits it and apologizes for disappointing her. Jane assures her of her love and support. Nora confesses they had sex only once, and she says that she hopes he will marry her when he returns, even though she wishes there were other ways to be “respectable” in society’s eyes. Jane argues that “a good man” would have married her first. Nora says the fault is hers, too, and reveals she told Alley she’s pregnant in her last letter but has still heard nothing. She fears the end of her nursing career and social disgrace.

Jane reveals that their parents are arriving that day for a visit. The sisters agree not to tell them about Nora’s pregnancy until after the holidays, hoping Alley will respond by then. Jane offers to raise the baby as her own so Nora can continue nursing. Overwhelmed and conflicted, Nora does not immediately decide whether she’ll accept the offer, but she appreciates her sister’s steadfast support. They resolve to face whatever comes together.

On December 5, 1917, in Halifax’s working-class Richmond neighborhood, Charlotte finishes the breakfast dishes in the Campbell house while her 15-year-old sister-in-law, Alice, refuses to help. Charlotte’s toddler, Aileen, sits in her highchair. Her husband, Frank Campbell, was killed at the Battle of the Somme. Charlotte lives with his family, and her mother-in-law, Emmeline, and Alice have disliked her from the start, partly because she is an orphan. They act as though her grief over her husband is unearned because she only knew Frank for two years. Charlotte contributes her widow’s portion from the Patriotic Fund to the household but saves Aileen’s smaller portion, hoping to secure a place of their own. When she asked to return to work at Dominion Textile, Mrs. Campbell refused, insisting a woman’s place is in the home.

After completing her chores, Charlotte takes Aileen on their daily walk, which is her only escape from her life of drudgery with her in-laws. She climbs toward Citadel Hill, her favorite spot to watch ships in the harbor, and tells Aileen that her father was a hero and loved her. She recalls Frank’s kind nature and the dreams they shared for after the war. On the way back, she passes Russell Street and sees the lot where fire destroyed her childhood home and killed her parents when she was nearly 18. Her loss left her numb for years until she met Frank. Aileen’s babbling draws her from her sorrow, and Charlotte resolves that, together, they can face anything.

On December 6, 1917, at 6:32 am, Nora prepares for her hospital shift, consumed by the secret she keeps from her visiting parents. The previous night, Jane had floated the idea of a quiet wedding to Alley, which only deepened Nora’s worry. In the kitchen, their mother, Maggie, shares her plans to visit the waterfront to see the ships, shop, and take Jane to lunch. Nora cannot join them because of work. Jane brings baby Clara to the waterfront, leaving Evelyn with a neighbor named Mrs. Thompson.

Before leaving for Camp Hill Hospital, Nora writes another urgent letter to Alley, pleading for a response about their baby. She gives it to Jane to mail and says she is still considering Jane’s offer to raise the child. At the hospital, Nora arrives a few minutes late and immerses herself in her duties. Her fellow nurses Jessie and Joan share the news that two ships collided in the harbor and that one of the ships is now on fire. Feeling isolated by her secret, Nora makes plans to go out with her colleagues the next night.

Suddenly, the air is sucked from the room, followed by a massive boom. The explosion throws Nora to the floor. Glass shatters, furniture topples, and chaos erupts. Matron Cotton helps her up, assesses her, and orders the staff to prepare for incoming casualties. Injured colleagues stagger in. A fierce protective instinct for her unborn child surges through Nora. She steadies panicked patients, enlisting men like Corporal Jenkins to help, while Sergeant Hammond sits rigid and dissociated. As the first survivors arrive, a doctor fears for those on the docks. Terror grips Nora as she recalls that her parents, Jane, and baby Clara were at the waterfront, but a sharp command pulls her back to duty as the hospital is overrun.

On December 6, 1917, at 8:22 am, Emmeline scolds Charlotte for not buying enough meat the day before and sends her out to purchase more. When Aileen cries, Emmeline criticizes Charlotte’s mothering as well. Upset, Charlotte heads out quickly with Aileen in the carriage.

On the streets, Charlotte senses unusual energy. People gather on corners, pointing toward the harbor. She asks a group of women from her church what is happening. They explain that a ship is on fire in The Narrows after a collision with another vessel. Charlotte mentions that her husband was killed at the Somme, and they offer their sympathy and invite her to join their knitting circle. She declines their invitation to walk closer to the waterfront with them and goes to her usual vantage at Citadel Hill for a better view.

Her unease grows at the spectacle and at the small explosions she hears, and she wonders what cargo the ship might carry. Pausing to soothe Aileen, Charlotte is overtaken by sudden silence. A deep rumble shakes the ground. A powerful force slams into her, and she is knocked unconscious.