The novel opens with a brief prologue set in July 1948, in which an unnamed figure stands poised to fire a gun. The moment before pulling the trigger is compared to jumping into cold water: full of power, full of the possibility of not doing it.
The story moves back to 1928, to Red Hook, Brooklyn, where Sofia Colicchio and Antonia Russo grow up in adjoining apartments. Their fathers, Joey Colicchio and Carlo Russo, work for Tommy Fianzo, a Mafia boss in Manhattan. Sofia is bold and quick-tempered; Antonia is quiet and observant. Together they are inseparable, though at school they are isolated because of their Family connections. Sofia's father is commanding and charismatic. Antonia's father, Carlo, is gentler and conflicted about his work. Their mothers, Rosa Colicchio and Lina Russo, bonded during their pregnancies and support each other when their husbands are away.
During a family beach trip, Carlo, who has been secretly skimming money and searching for a way out of the Family, is summoned by a late-night phone call from Tommy and never returns. Back in Brooklyn, Tommy reveals that Carlo was stealing and frames the disappearance as a necessary solution, offering Joey control of his own section of Brooklyn in exchange for a monthly payment. At Carlo's funeral, held without a body, Lina publicly confronts Joey and tells young Antonia that Joey is responsible for her father's death.
Lina collapses into grief, renouncing the church and withdrawing from the world. Antonia begins attending Sunday dinners at the Colicchio home. Joey arranges a laundry job for Lina while secretly paying her rent. Rosa gives birth to a second daughter, Frankie, and both girls help care for the baby. As they enter their preteen years, Sofia develops a tough exterior while Antonia retreats into books.
At 14, Sofia and Antonia drift apart. Sofia cycles through popular friends and refuses to attend church. Antonia excels academically and secretly starts attending Sunday Mass, dreaming of college and a life beyond the Family. In the summer of 1940, as Italy enters the war, the two reconnect during a tense Sunday dinner and argue about the Family's morality. Sofia declares the work is wrong; Antonia counters that the Family pays both their rents. Sofia realizes she is not just angry at the Family but curious about it, while Antonia reluctantly abandons her dream of escape.
That fall, Antonia meets Paolo Luigio, a young man delivering forged passports as part of Joey's wartime smuggling operation, which transports Jewish and other refugees from Europe hidden among Italian food imports. They begin a quiet courtship that Antonia keeps secret. Joey hires Saul Grossman, a young German-Jewish refugee who fled Berlin and now works at a Lower East Side deli, as an assistant for the operation. Sofia sees Saul across a Sunday dinner table and is captivated. Antonia eventually tells Lina about Paolo, and in a pivotal moment, Lina chooses not to repeat her pattern of fear, asking Antonia to tell her about him. When Antonia calls Sofia with the news, Sofia hides a pang of jealousy.
Sofia kisses Saul impulsively after engineering an encounter in a hallway. After Pearl Harbor in December 1941, they sleep together. By February 1942, Sofia discovers she is pregnant. She announces the news at a family dinner, and Joey decrees that Saul will convert to Catholicism, take the Colicchio surname, and marry Sofia. Later that night, Joey holds a gun to Saul's chest and delivers what he calls the first rule of fatherhood: "You don't get to die now. It's not about you" (172). Antonia marries Paolo in the spring, with Joey walking her down the aisle. Sofia and Saul marry privately.
Throughout her pregnancy, Sofia wrestles with a doubt she cannot voice: She is not sure she wants to be a mother. When she gives birth to a daughter she names Julia, she is struck by the evidence of her own power. Antonia gives birth to a son, Robbie, but the delivery is traumatic, and she sinks into severe postpartum depression lasting months. Sofia comes every day through the winter, caring for both babies. One February morning, Antonia wakes laughing, feeling the smallest bit of herself return. By April, she picks up Robbie and truly feels his weight for the first time, whispering that she is ready to be his mother.
In 1943, Joey buys a brownstone in Carroll Gardens. Sofia and Saul take the first floor; Rosa and Joey move upstairs. Joey begins taking Saul to monthly meetings with Tommy Fianzo at the Red Hook dock building. Sofia, restless with domestic life, secretly reads Saul's work notes and tails him around Manhattan. Joey discovers this and offers her a job. Her first assignment, a lunch with a corrupt detective on the Family payroll, reveals her natural talent for the work. Meanwhile, Saul commits his first act of violence during a collection job and is disturbed not by guilt but by how easy it feels.
During a week when both families are staying together, Antonia tells Saul the full truth about Carlo's death: Tommy Fianzo had Carlo killed for trying to leave, and Joey made a deal afterward. Saul realizes Sofia lied to him for years. Not long after, Eli Leibovich, a rival Jewish crime boss, approaches Saul and appeals to their shared heritage, offering cultural belonging and wanting intelligence about the Fianzo dock operations. Saul accepts and begins passing details to Eli. Joey, sensing the need for a successor, promotes Saul to second-in-command. Saul accepts despite his guilt.
By 1947, Saul is living a double life. Tommy Fianzo Jr. has taken over the monthly meetings and treats Saul with open contempt. Sofia has settled into her role managing Family operations, and Joey gives her a pearl-handled revolver she keeps in her nightstand. Antonia discovers she is pregnant again and confides in Sofia, admitting she fears she made all the wrong choices. Paolo, bitter about being passed over for promotion in favor of Saul, grows distant, and their marriage fractures.
After a meeting, Saul carelessly drops a slip of paper with notes about the dock operation, and Tommy Jr.'s doorman finds it. Tommy Jr. contacts Paolo, reveals Saul's betrayal, and offers him a promotion if he kills Saul. Paolo confronts and beats Saul but cannot go through with it. Sofia discovers Saul's notebooks in his locked desk, dials a phone number written inside, and reaches Eli, confirming the betrayal. Before dawn, she goes alone to the Fianzo dock building and offers Tommy Jr. the notebooks, containing Saul's intelligence on Eli, in exchange for Saul's life. As Tommy Jr. reaches for them, Saul bursts in and Tommy Jr. pulls a gun on Sofia.
Antonia and Paolo go to Lina, who urges them to fight for Saul. Antonia storms into the Colicchio apartment, and Rosa reveals where Sofia and Saul have gone. Antonia retrieves Sofia's revolver and rushes to the docks with Paolo. At the waterfront, she finds Saul on his knees, Tommy Jr. holding a gun, and Sofia nearby. Antonia shouts, Tommy turns, and she fires. The scene mirrors the prologue. Standing with the gun, Antonia looks out over the East River and sees Carlo's face for the first time since childhood. He smiles and disappears into the water. Sofia and Antonia embrace. Behind them, Saul and Paolo begin covering the body, already planning how to frame the killing. It begins to rain.