The novel opens on the wedding day of Greer Galloway as she stands before the doors of a church, reading the Bible verse "Love endures all things" and wondering if God is sending her a warning. Walking down the aisle to marry President Maxen Ashley "Ash" Colchester, she sees his best man and vice president, Embry Moore, beside him. She notices bite marks on her own thighs, a fresh mark on Embry's neck, and the lace of her panties tucked into Ash's pocket, all evidence of a shared sexual encounter before the ceremony. The narrative then spirals backward to explain how these three became entangled.
Eighteen years earlier, seven-year-old Greer attends a charity gala with her grandfather, Leo Galloway, a former vice president of the United States. Leo introduces her to Merlin Rhys, a young Welsh consultant joining Leo's political party. Merlin studies Greer's face and warns her to keep her kisses to herself, claiming that a single kiss from her could swing the world "from friendship to anger. From peace to war" (7). He also expresses sorrow about her parents, though they are still alive. That night, Greer dreams of a train plunging from a collapsing bridge. The next morning, her grandfather delivers the news: Carpathian separatists blew up a train bridge, killing her parents. Merlin's prediction proves terrifyingly accurate, and Greer vows never to kiss anyone.
Greer moves in with Grandpa Leo in Manhattan and at 14 enrolls at Cadbury Academy in England alongside her cousin Abilene. Greer is quiet and bookish; Abilene is vivacious and socially dominant. Greer serves as Abilene's caretaker while privately remaining bound by Merlin's warning.
The novel shifts to the present. Greer, now in her mid-twenties, teaches Arthurian Literature at Georgetown University. Vice President Embry Moore appears one night and invites her to dinner. They have not spoken in five years. Over dinner, Embry reveals that President Colchester wants to meet with her, and she agrees.
A flashback reveals the origin of their connection. At 16, Greer meets Captain Maxen Colchester, a 26-year-old American soldier, at a birthday party in London. While cleaning up broken glass, she cuts her finger, and Ash draws the wounded fingertip into his mouth, an act that awakens her sexually. She intuits from the shadows under his eyes that he has combat-related insomnia, and her perceptiveness stuns him. He kisses her, her first kiss, until Merlin interrupts and pulls Ash away.
Over the following year, Greer sends Ash emails that go unanswered. War is declared against the Carpathian separatists, and Ash's famous rescue at the village of Caledonia makes him a national hero. Greer follows his career obsessively. On her 17th birthday, tipsy and alone, she writes a sexually explicit email describing her fantasies of dominance and submission, then vows it will be her last.
In the present, Ash and Greer reunite at her church. He tells her he never stopped thinking about her, even during his marriage to his late wife, Jennifer Gonzalez. He asks Greer to be his, and she admits she already is. That night at the White House, Ash establishes their dominant-submissive dynamic, setting the safe word "Maxen." He produces a wooden box containing her old emails, printed and worn from years of handling, memorized word for word. Their first encounter combines rough dominance with tender aftercare. Greer spends the night, and Ash falls asleep beside her for the first time in 14 years, his chronic insomnia lifted by her presence.
A flashback returns to when Greer was 20. In Chicago, she unexpectedly encounters Ash, and the attraction is overwhelming. That evening, Merlin tells Greer that Ash proposed to Jenny the day before. Devastated, Greer tries to flee and crashes into Embry, Ash's best friend. Embry charms her and takes her to Navy Pier, where on a Ferris wheel they confess their parallel heartbreaks. She asks him to make her forget, and he kisses her. Back at his hotel, they have sex; Greer reveals mid-act that she is a virgin. Afterward, Embry is tender, promising to see her again, but he never calls. Greer vows never to trust anyone again.
In the present, Merlin visits Greer and reveals that Ash is the illegitimate son of President Penley Luther, Leo Galloway's former running mate, who abandoned Ash to foster care to avoid scandal. Ash learned this truth only at Jenny's funeral. Merlin confesses he introduced Ash to Jenny specifically to keep him away from Greer.
At a state dinner, Senator Morgan Leffey, Embry's stepsister, aggressively implies she has a sexual history with Ash. After the dinner, Ash orchestrates a charged three-way scene in the Residence, the White House's private living quarters: He orders Greer to kneel and wait, then has her ride his thigh to orgasm while Embry watches, before ordering Embry to masturbate into Greer's ball gown.
Six weeks later at Camp David on Christmas Eve, Ash confesses that Morgan is his half-sister. They share the same mother, Imogen Leffey, and he unknowingly committed incest during a wartime affair. He describes a wartime choice between rescuing children and adults that has haunted him since. Despite these revelations, Greer tells Ash she loves him, and he proposes. That night, they consummate their relationship, combining intense dominance with tender aftercare. Greer confesses that Embry was her first sexual partner, and Ash admits to complex jealousy, both possessive and aroused by the thought. Later, Greer discovers Ash and Embry kissing under the mistletoe, a familiar kiss that is clearly not their first.
At a diplomatic meeting in Geneva, Greer is sexually harassed by Carpathian President Melwas Kocur during a dance, and Embry intervenes. Dancing with Embry afterward, Greer tells him she saw the Christmas Eve kiss. They confess their love, and Embry discloses his sexual history with Ash, which began after Caledonia and continued off and on for years. Greer confronts Ash, who admits he still loves Embry and reveals he proposed to Embry twice, only to be refused both times. Ash warns Greer that Abilene tried to kiss him at the Geneva dinner and declared she would make a better wife. They agree to complete honesty and no sexual contact with Embry until all three can talk, but the conversation never happens.
On the wedding day, Embry arrives at Greer's bridal suite with a "wedding present" from Ash: Via phone, Ash orders Greer to let Embry pleasure her while he listens. At the reception, Embry leaves early, unable to endure more. Ash tells Greer he wants Embry to join them on their wedding night.
In the hotel suite, Embry arrives. Ash kisses him and tells him he loves him. The three promise to try to make their relationship work. Their consummation is intense and emotional, and afterward Ash tells Greer what happens next is that they all live happily ever after.
The happiness is short-lived. Greer wakes in the middle of the night to a text from Abilene asking her to come to the hotel lobby. Earlier, during the ride from the reception, Greer had texted Abilene the hotel's name. In the hallway, she discovers all Secret Service agents are absent from their posts. Before she can return to the room, a man in a hotel employee uniform blocks her path. She recognizes him from the Carpathian diplomatic dinner. The novel ends on this cliffhanger, implying Greer has been lured into a trap connected to Carpathian President Melwas Kocur.