Hanna Heller (Saoirse Ronan) is a 15-year-old girl who lives with her father, Erik Heller (Eric Bana) in rural northern Finland, near Kuusamo. The film opens with her hunting and killing a reindeer, first by shooting it with an arrow that just misses its heart, and then killing it with a handgun.Since the age of two, Hanna has been trained by Erik, an ex-CIA operative from Germany, to be a skilled assassin. He teaches her hand-to-hand combat and drills her in target shooting. He left the agency, going incognito into the Arctic. Erik knows a secret that cannot become public, and is being sought after by Marissa Wiegler (Cate Blanchett), a senior CIA officer, who wants to eliminate Erik. Erik has trained Hanna with the intent that she will kill Marissa. Hanna reads a bloodstained Grimms' Fairy Tales book frequently, has a great deal of encyclopedic knowledge, and is fluent in several languages. Due to her training away from civilization, she has never come into contact with modern technology or culture, and is unfamiliar with music or electricity. She has memorized a series of fake back-stories for herself to be used "when the time comes".One night, Hanna tells Erik that she is "ready" to face their enemies. Erik digs up a radio beacon that will alert the outside world to their presence. Warning Hanna that if Marissa ever finds her, she "won't stop until you're dead. Or she is", he reluctantly allows Hanna the freedom to make her decision. After some consideration, Hanna flips the switch. Erik leaves, instructing her to meet him in Berlin. Hanna kills two of the special forces team when they enter the cabin and then waits for the rest, knowing that they will assume her father to have killed the pair before escaping.Hanna is taken to an underground CIA complex. Marissa is suspicious of Hanna's request to talk to her, and sends in a body double (Michelle Dockery) instead. Hanna asks the body double where she met her father. The double, who is being fed answers through an earpiece by Marissa, answers the questions correctly, and Hanna starts to cry and crawls sobbing into the lap of the double, which makes the officials uneasy. They send soldiers and a doctor to her cell to sedate her. As they enter the cell, Hanna kills the double, and several others (stealing a handgun from one), breaks free through the ventilation system and escapes.She finds herself on the run in the Moroccan desert, where she meets Sebastian (Jason Flemyng) and Rachel (Olivia Williams), a bohemian British couple on a camper-van holiday with their teenage daughter, Sophie (Jessica Barden), and their younger son, Miles (Aldo Maland). She sneaks into the family's camper-van and hitches a ferry ride to Spain with the goal of reaching Germany. The family is nice to her, and she and Sophie become friends, and spend some time together, even sharing a kiss.Marissa hires Isaacs (Tom Hollander), a former agent, to capture Hanna. Hanna travels with the family as they drive north. Isaacs and two skinheads trail them and eventually corner Hanna and the family in France, but she manages to escape, killing one of the men. Marissa arrives and interrogates the British family, finding out that Hanna is heading to Berlin, her place of birth. Arriving at the address her father had told her, Hanna meets with Knepfler (Martin Wuttke), an eccentric old magician and a friend of Erik's, who lives in a Grimms' Fairy Tales-themed house in an abandoned amusement park. It is Hanna's 16th birthday and Knepfler makes her breakfast. Hanna plans a rendezvous with her father. However, Marissa and Isaacs arrive. Hanna escapes, but not before she overhears comments that suggest Erik is not her biological father.Later, Hanna meets her father at her German grandmother's apartment, whom Marissa had already shot, demanding he tell her the truth, and he reveals that he is not her father. Erik once recruited pregnant women into a program where their children's DNA was enhanced in order to create super-soldiers. The project was shut down, with almost all of its subjects eliminated. In a flashback, Marissa is seen firing on a car, carrying Johanna Zadek, Hanna's mother, two year old Hanna and Erik. The car crashes but the trio flees. Marissa follows, shooting Johanna as she lies on the ground but Erik escapes with Hanna into the woods.Marissa and Isaacs arrive, intent on killing them; Erik acts as a distraction to allow Hanna to escape. Erik kills Isaacs in a brutal fight, and is shot by Marissa, who returns to the Grimm house. Hanna is there, having just discovered Knepfler dead. After a chase, Hanna and Marissa confront one another. Hanna pleads for an end to the killing, saying she does not want to hurt anyone else. Marissa says she just wants to talk, but Hanna starts walking away. Marissa shoots Hanna, who responds by shooting her with an arrow she pulled from Knepfler's body. Hanna is knocked to the ground by a bullet. She gets up, gets her bearings and follows Marissa into a tunnel, noticing a deer, and then seeing her fleeing up a nearby water slide. An unarmed Hanna chases Marissa to the top of the slide's stairs, as she shoots at her. Near the top, it becomes clear that Hanna's arrow did more damage than Marissa's bullet, and a disoriented Marissa falls and slides down the water flume just as she is about to shoot Hanna, dropping her handgun. Hanna follows the wounded Marissa, picks up the dropped gun, and shoots her in the heart. The bookend scene mirrors the opening of the film in which Hanna hunts and kills the reindeer.