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.

Following her capture by Marissa's men, Hanna must fight to escape from the Moroccan CIA facility and join Erik in Berlin. Along the way, she meets Sophie, a British teenager on holiday with her family, who gives Hanna her first proper taste of the real world and the thrill of adolescence. Yet despite this glimpse at normality, the threat of Marissa and her operatives is never far behind.