Set in 1902 New York, the novel follows two young women whose lives converge at Ellis Island, the federal immigration station where millions of newcomers entered the United States: Francesca Ricci, a Sicilian immigrant fleeing her violent, alcoholic father, and Alma Brauer, a German American reluctantly sent to work as a matron at the station.
Francesca and her younger sister, Maria, endure a brutal winter crossing in steerage, the cheapest belowdecks quarters. Maria grows sicker by the day with fever and fluid in her lungs. Francesca has spent her life shielding Maria from their father, Paolo Ricci, whose fire poker left a terrible scar on Francesca's back. Their mother disappeared years earlier, and a kind Catholic nun, Sister Alberta, helped raise them. When the ship arrives in New York Harbor, Francesca carries little more than a stolen medallion of the Virgin Mary and a calling card from Marshall Lancaster, a wealthy English gentleman who showed her kindness aboard the ship.
Alma, twenty-one, lives above her family's bierhaus, or beer hall, on Orchard Street in Kleindeutschland, a German enclave on Manhattan's Lower East Side. She secretly studies Italian and Russian, defying her stepfather, Robert Brauer, who disdains her as a burden. When Robert arranges a job for Alma at Ellis Island through Inspector John Lambert, a bierhaus regular, she is horrified at the prospect of working among the immigrants her family regards with prejudice.
At Ellis Island, Francesca and Maria undergo humiliating medical exams before a room of male doctors. Maria, gravely ill, is separated from Francesca and sent to the hospital on a neighboring island. Without a male relative or an employment letter, Francesca faces deportation. She lies, claiming an uncle in Chicago will come for her, buying herself time. Alma, assigned to translate for the sisters, witnesses their ordeal and begins to feel unexpected sympathy for the immigrants' desperation.
Maria's condition deteriorates rapidly. Before she dies, she makes Francesca promise to thrive in America for them both. Devastated, Francesca confesses to Alma that the uncle was a fabrication, that she is entirely alone, and shows Alma the burn scar on her back. Moved by Francesca's courage, Alma vows to help her pass inspection. She asks her mother, Johanna, to sign an employment waiver, but Johanna refuses, unwilling to risk the family's reputation for a stranger.
Francesca remembers Lancaster's calling card, and Alma and her older brother, Fritz, visit the Lancasters' Park Avenue home. After Alma reveals the extent of Francesca's abuse, Lancaster agrees to hire her as a cook and signs the waiver. At the final inspection, however, the inspector implies Francesca's papers may be forged and demands a sexual encounter as his price for letting her pass. Francesca, understanding that refusal means deportation back to her father, agrees. She dissociates during the assault, retreating into a mental fortress built from years of abuse. With his signature secured, she descends the stairs to freedom.
Francesca begins working in the Lancaster kitchen under the head cook, Claire Deveaux, who becomes a close ally. Mrs. Lancaster is furious to recognize Francesca as the steerage passenger who once took water from her first-class table but grudgingly allows her to stay after tasting her cooking. Meanwhile, at Ellis Island, a new commissioner, William Williams, arrives to root out staff corruption. Alma witnesses inspectors accepting bribes and vendors shortchanging immigrants but is warned to stay quiet. She befriends Jeremy Kerrigan, an Irish interpreter who encourages her dream of becoming an interpreter, and Helene Bach, a fellow matron who becomes her closest confidant.
Fritz and Francesca grow closer through nightly visits and Sunday picnics in Tompkins Square Park. Fritz falls openly in love with Francesca, and she begins to trust him as she has never trusted a man. During a rainstorm, they share their first kiss. But Francesca soon realizes she has not had her menses in over nine weeks and understands she is pregnant from the inspector's assault.
Meanwhile, Robert and Johanna accept Lambert's marriage proposal on Alma's behalf without consulting her. Alma feels trapped, knowing defiance could leave her homeless. At a Sunday picnic, Francesca sees Lambert and recognizes him instantly as the inspector who assaulted her. She flees, sick with shock, realizing Alma's fiancé is the father of her unborn child.
During a police raid at a beer hall where anarchists are gathering, Fritz is arrested. In the chaos, Francesca stumbles, and Alma catches her, feeling the bump of her pregnant belly. Francesca tells Alma the full truth: Lambert forced the encounter as the price of her entry into the country. Helene confirms she had long suspected Lambert of assaulting immigrants. Alma resolves to break the engagement.
Francesca tells Fritz about the pregnancy. He is furious at the unnamed inspector but not at Francesca. He asks for time to think, and his hesitation devastates her. Alma confronts her parents, revealing Lambert's history of abuse. Robert dismisses the claims and gives Alma an ultimatum: Marry Lambert or leave the household. Alma chooses to leave.
Alma approaches Mrs. Keller, her supervisor at Ellis Island, who reveals Lambert's long record of misconduct, including impregnating a French immigrant he then had deported and driving an Italian woman to suicide. Alma goes to Commissioner Williams and strikes a deal: She will provide a witness in exchange for the chance to train as an interpreter. She persuades a reluctant Francesca to return to Ellis Island to testify.
The return is agonizing for Francesca, battered by memories of Maria's death and the assault. Before they reach Williams's office, Lambert spots them, recognizes Francesca's pregnancy, and threatens deportation. Francesca kicks him and unleashes a torrent of insults. Alma declares the engagement over. Williams, drawn by the commotion, orders them all to his office, where Francesca tells her story. Lambert denies everything, but her visible pregnancy stands as evidence. Williams commits to an investigation.
Knowing the investigation could threaten her immigration status, Francesca decides to leave for Chicago. Mrs. Lancaster, upon learning of the pregnancy, fires her gently but gives her a reference letter and, in a private moment, a gold wedding band, revealing that she, too, was once an unwed mother. Mrs. Cheedle, the Lancaster housekeeper, also provides a reference.
Francesca finds Fritz at a labor strike near the subway construction site. Amid the roaring crowd, Fritz tells her he does not care about the baby, that he loves her and wants to be part of her life. Francesca, weeping, tells him she must leave the city. They kiss amid the chaos, but she walks away, honoring her promise to Maria.
In the epilogue, set weeks later, Alma has moved in with Helene, is saving her wages, and plans to enroll at New York University to become an interpreter. Fritz, without telling his parents, has arranged a work transfer to Chicago to find Francesca, who does not yet know he is coming. Alma sees him off at the train station, and they embrace, proud of the paths they have chosen. Alma walks to her new home, alone and free.