In a covert Romanian facility, Erik Heller evades security to rescue baby Hanna. 15 years on, father and daughter live deep in the Polish forest. Erik has trained Hanna to be an incredible killer and hunter. Yet, keen to grow beyond the boundaries of her isolated world, she begins to venture away from home. This attracts the attention of CIA agent Marissa Wiegler, who has hunted Hanna since birth.

Hanna befriends a vacationing family and in short order is exposed to the indulgences of teen life she had been deprived of. Her father, Eric, continues on a journey to eventually meet up with Hanna.

Hanna and Erik are finally reunited in Berlin, where he introduces her to his old army friends and allies. As they hide out in a disused military bunker, planning their next step, Hanna begins to learn more about her father's past. However, having glimpsed a normal family life with Sophie, she becomes increasingly frustrated at her own and at the restrictions Erik imposes on her. Meanwhile, having tracked them down to Berlin with the help of Jacobs, Marissa and her CIA colleague Meisner arrive in the city. They begin to delve into Erik's past, seeking old connections ...

Erik is holding Marissa prisoner in a disused water tower, trying to negotiate a deal to get him and Hanna safely out of Berlin. Jacobs attempts to track Marissa down but quickly discovers who has the upper hand. Meanwhile, Hanna hides out with Dieter and his family, much to the concern of Dieter's wife Sima. Desperate to know more about what her father is up to, Hanna follows Dieter on a nocturnal trip to the water tower. In doing so she begins to learn that there is more about Erik's past than he has been telling her. As Erik's escape plan begins to come together, ...

Still reeling from her revelations about Erik, Hanna hides out in suburban London with Sophie who is keeping her new friend secret from her parents. Sophie is housing Hanna in the family caravan in a nearby garage. Concerned at Hanna's grief-like state, Sophie persuades her to attend a school party, where Hanna meets Sophie's friends including a very cute boy named Anton, who she quickly realises Sophie also feels very strongly about. Meanwhile, unable to go to the hospital for fear of capture, Erik's friends desperately try to save him from the life-threatening ...

Sophie and Hanna's relationship begins to turn sour over their shared interest in Anton. In the fallout from this argument, Marissa arrives at Sophie's house pretending to be Hanna's mother. Hanna finds herself torn between endangering Sophie and her family, or giving up her own freedom and going with Marissa. Meanwhile, a captured Erik is brutally interrogated by Sawyer and his men.