Raised in the isolated expanse of the Arctic wilderness, a 16-year-old girl has spent her entire life training to be an assassin under the guidance of Erik, her father and former CIA operative. Taught to hunt, fight, and survive in extreme conditions, she is fluent in multiple languages and possesses the skills and knowledge far beyond her years. Living off the grid, she is unfamiliar with modern society and technology. Her education and physical conditioning are all aimed at one purpose: completing her first mission in the outside world. When she declares she is "ready," her father gives her a transmitter that, once activated, will alert the CIA to their location and set her mission in motion.

Once she flips the switch, their tranquil life is shattered as they become the targets of a relentless pursuit led by Marissa, a high-ranking intelligence operative with an enigmatic connection to Hanna and Erik. Marissa dispatches a team of agents to capture them, leading to a separation of father and daughter. Alone for the first time, Hanna must navigate the real world while evading the agents on her tail. Her journey takes her across Europe as she seeks to reunite with her father and complete her mission, facing the challenges of a complex world she is experiencing for the first time and uncovering startling revelations about her own existence.