Anna Foster (Mandy Moore) is the daughter of President James Foster (Mark Harmon) and First Lady Michelle Foster (Caroline Goodall). After Secret Service agents ruin a first date, Anna demands some freedom. For their upcoming trip to Prague, the president agrees to assign only two agents to watch over Anna, whose Secret Service codename is Liberty. In Prague, Anna and her friend Gabrielle La Clare (Beatrice Rosen) attend a concert, where Anna discovers numerous agents in the crowd. Believing her father has broken his promise, Anna eludes her protectors with Gabrielle's help.
Outside the theater, Anna meets Ben Calder (Matthew Goode), and asks for a ride on his motorbike. They go to a bar, where Anna proceeds to get drunk. Unknown to Anna, Ben is a Secret Service agent, and he informs agents Alan Weiss (Jeremy Piven) and Cynthia Morales (Annabella Sciorra) where Anna can be found. When the president learns of her behavior, he instructs Ben to guard Anna without revealing his true identity—giving her the illusion of freedom with a guarantee of safety.
Believing she is finally free, Anna jumps into the Vltava River naked, mistaking it for the Danube. As Ben rushes in to retrieve her, Weiss and Morales "buy" a tourist's camera containing pictures of the skinny-dipping Anna. Later, Anna and Ben climb a rooftop to watch an Offenbach opera being shown in a plaza. Weiss and Morales observe from a nearby rooftop. Anna falls asleep with Ben watching over her.
The next morning, Anna calls her parents. Initially relieved that his daughter is safe, the President's tone changes when he is shown photos of her skinny-dipping. Outraged at her father's tone and learning that he traced her call, Anna decides she will go to the Love Parade in Berlin. She and Ben board a train, where they meet Scotty McGruff (Martin Hancock), a flighty romantic who gives them a stack of Six Million Dollar Man stickers, instructing them to post them in random places, and one day when they are unhappy, they may come across one and it will make them smile. Ben discovers that they have boarded a Venice-bound train going in the opposite direction from Berlin.
In Venice, after checking in with agents Weiss and Morales—who are now growing closer romantically—Ben joins Anna and McGruff and together they explore the city. Later, after McGruff leaves, Anna realizes he has stolen her wallet. When Anna is recognized by tourists, she and Ben run off. With no money, they tell a kind-hearted gondolier, Eugenio (Joseph Long), that they recently married against her parents' wishes. During the free gondola ride, Ben kisses Anna to hide her from their pursuers. When he learns the "newlyweds" have no place to stay, Eugenio invites them to his house, where they are welcomed by his mother, Maria (Miriam Margolyes). That night, thinking their kiss was heartfelt, Anna offers herself to Ben, but he rejects her advances.
The next day, Eugenio drives them to the Austrian border, as Weiss and Morales show up at Maria's house and learn from Maria that Anna and Ben are married, which is then reported to Anna's parents. Upset at Ben's rejection, Anna hitchhikes a ride in a truck, leaving Ben to chase her through the Austrian countryside. Anna comes to a bridge, where she meets the Jumping Germans, a bungee jumping group. Ben arrives just as Anna is being strapped into the harness, and he insists on jumping with her. They jump from the bridge, harnessed together in a tight embrace.
Later that evening at the Jumping Germans' camp, Anna and Ben sit by a fire and eat s'mores. After one of the Germans, Gus Gus (Adrian Bouchet), asks Anna to share his tent for the night and she refuses, she flirts with Ben, who rejects her advances again. Upset by his rebuff, she declares that she will share Gus Gus's tent after all. In a jealous panic, Ben finally admits his feelings for Anna. As Ben's phone rings, he tosses it aside, and they spend the night together.
The next day, Anna and Ben make it to the Love Parade in Berlin. Anna meets up with Gabrielle while Ben goes off in search of a phone booth. As Ben tries to explain his actions on the phone to his fellow agents, Anna comes up behind him and discovers he is a Secret Service agent. Enraged at the apparent betrayal, Anna runs off, only to be harrassed by a group of men who recognize her. Ben comes to her rescue and carries her to a waiting helicopter, which takes off and leaves Ben on the ground alone.
Back at the White House, while preparing for college, Anna reveals to her mother that her heart is "a little bit broken." At college, with Weiss and Morales still protecting her, Anna sees a Six Million Dollar Man sticker and smiles in spite of herself, reminded of her European adventure. By now, Weiss and Morales have fallen in love and plan to marry. They acknowledge he will need to find another partner.
On her Christmas break, Anna visits her father who tells her that Ben resigned from the Secret Service and is now working as a photographer in London. Anna travels to London on an exchange program to Oxford University and visits Ben at an opera, where they kiss and reconcile, with Agent Weiss and his new partner looking on. Anna and Ben leave the theater and escape on his motorbike.