Nineteen-year-old Francesca Rossi is the only child of Arthur Rossi, head of the Chicago Outfit, the city's Italian-American organized crime network. Raised in a gilded cage, she attended boarding school in Switzerland and was forbidden from college, groomed to marry a suitable Outfit man. She has loved Angelo Bandini, a young man from a powerful Outfit family, since childhood. Her family keeps a carved wooden box containing three fortune-telling notes, each written by the last Rossi bride for the next. Before a masquerade gala at the Art Institute of Chicago, she reads the first note: Whoever kisses her tonight will be the love of her life. She is confident Angelo will fulfill the prophecy.
At the gala, a rude stranger humiliates Francesca at dinner, mocking her lack of education. He identifies himself as Senator Wolfe Keaton, newly elected at age 30. Angelo confirms his feelings but cannot steal a private kiss. Later, Francesca stands alone on the museum steps when a man wearing Angelo's gold mask approaches and kisses her. She gradually realizes it is Wolfe, who stole Angelo's mask. Angelo witnesses the aftermath and storms off.
The next morning, Wolfe meets with Arthur and their attorneys, then announces Francesca is betrothed to him. His perspective reveals his true motivation: He has hated Arthur since childhood and planned the man's downfall for years. He chose Francesca after noticing she was Arthur's greatest weakness, forcing Arthur to his knees with undisclosed but devastating evidence. He intends to use her to clean his reputation while destroying Arthur's empire.
Francesca is installed in a separate wing of Wolfe's mansion under the care of Ms. Sterling, his elderly housekeeper. She begins a hunger strike. The second note predicts that the next man to feed her chocolate will be the love of her life. She hides it, but Wolfe finds and reads it, then sends her a Godiva chocolate basket, manipulating the tradition. He forces her to attend a political wedding, where she spots Angelo with Emily Bianchi as his date. After Angelo and Francesca share an agonizing goodbye, Wolfe sleeps with Emily as retaliation for what he assumes Francesca and Angelo did.
Back at the mansion, Francesca destroys Wolfe's wardrobe with garden shears. He proposes a deal: If she eats, plays the dutiful wife, and entertains his guests, he will send her to Northwestern, something her parents forbade. She agrees but adds conditions: mutual fidelity and that he must not read her remaining notes. Francesca begins studying Political Science, fills her time with gardening, horseback riding, and piano. Wolfe escalates his war against Arthur, destroying a property containing cocaine and flooding Chicago with additional police.
Their dynamic shifts at a dinner at the Rossi home, where Arthur viciously belittles Francesca and hurls a wine glass at the wall. Wolfe threatens him, and Francesca, for the first time, crawls into Wolfe's lap seeking comfort. A physical relationship develops, though she halts before sex, terrified because she is secretly a virgin despite having lied about being experienced.
Arthur arranges a shooting at a school event targeting Wolfe, who disarms the gunman and keeps Arthur's involvement secret. Arthur then hosts an engagement party, inviting Angelo and Wolfe's former fling, journalist Kristen Rhys. Angelo, heartbroken after Francesca confides she is warming to Wolfe, sleeps with Kristen. Wolfe sees Angelo emerge disheveled and assumes Francesca was with him. On the drive home, he calls her a whore and demands she prove her loyalty through sex. They have sex violently, and mid-act Wolfe discovers she is a virgin. Horrified, he tries to stop, but Francesca forces him to finish. He whispers he will never doubt her again. The following night, consumed with guilt, he breaks his lifelong rule against kneeling to give her pleasure, beginning to rebuild trust.
On the wedding day, Ms. Sterling reveals to Francesca that she is Wolfe's biological mother, recovering from alcohol addiction, whose neglect contributed to the tragedy that orphaned him. She tells Francesca that Wolfe is capable of love but everyone he loved is dead. At the reception, Francesca intervenes when Arthur tries to strike her mother, Sofia, and takes the blow herself. Wolfe, furious, cuts Arthur's palm and uses his blood for the traditional wedding sheets, protecting Francesca's dignity.
A week later, soldiers loyal to Angelo's father, Mike Bandini, an Outfit leader, chase and ram Francesca's car on the highway. She is bruised but not seriously hurt. That night, Wolfe sleeps in her bed for the first time, breaking his rule against sharing a bed. He then confronts Mike Bandini, warning that further harm to Francesca means war.
At his cabin on Lake Michigan, Wolfe reveals he pursued law because Arthur robbed him of justice. They have tender, consensual sex for the first time. Wolfe finishes inside her, calculating she is not ovulating, but neither accounts for a Plan B pill having shifted her cycle. Their relationship transforms into a genuine partnership.
Five weeks later, Francesca discovers she is pregnant. Angelo confesses he let Wolfe believe they had slept together at the engagement party, hoping to break them up. Then Kristen reveals Wolfe's full backstory: He was born Fabio Nucci and witnessed Arthur shoot and kill his older brother Romeo, a police officer, when Wolfe was a child. The Keatons adopted him and changed his name. Arthur later orchestrated an explosion that killed Wolfe's adoptive parents. Kristen insists Wolfe always planned to discard Francesca.
Shattered, Francesca opens the third note: The love of her life will shelter her from the storm. She stands in the rain outside school, waiting for Wolfe. He does not come. Angelo does, sheltering her. She tells him she is pregnant and wants a divorce. He kisses her publicly, and Kristen records it. The images go viral. Wolfe confronts Francesca, removes his ring, and reveals he manipulated the first two notes. He argues the third should apply to him, since he sheltered her from her father and the Bandinis. To retaliate, he takes another woman to a gala. Francesca warns that if he walks out, she will not be there when he returns. He leaves.
Wolfe cannot bring himself to be unfaithful. He returns to find Francesca gone and her pregnancy test hidden in a pillowcase. For a week, Arthur's guards turn him away. Ms. Sterling visits Francesca, confirms Wolfe's past, and tells her that Wolfe found the test and was devastated. Wolfe arrives at the Rossi house with a search warrant. Arthur demands he kneel, mirroring the humiliation Wolfe once forced on him. Despite his lifelong vow, Wolfe kneels before the man who killed his family and declares Francesca is the most important thing in his life. Francesca, eavesdropping, faints.
She wakes in Wolfe's arms. He tells her he wants the baby and is in love with her. She asks for time to rebuild their relationship on equal terms. Over the following month, they date properly and attend her first prenatal appointment together. Francesca's mother announces she is divorcing Arthur. Francesca tells Wolfe she is ready to come home. He has built a nursery beside their shared bedroom and proposes again. She accepts.
Four years later, they baptize their second child, Joshua Romeo Keaton. Arthur is in prison for the attempted murder of Francesca's mother, Sofia. Angelo is happily engaged. Six years after the main events, the family prepares to move to Washington, DC: Wolfe has been elected President of the United States.