A brilliant but asocial mathematician named John Nash arrives at Princeton University, intent on making an original contribution that will set him apart. His roommates and the educational environment pressure him, while he struggles to find his unique path. John eventually creates a groundbreaking economic theory, which garners the attention of the mathematics community and secures him a position at MIT, as well as a consulting role at the Pentagon, where he is tasked with breaking Soviet codes during the Cold War.

John's personal life also flourishes when he meets and marries Alicia, a student of his. However, his contribution to the Pentagon draws him deeper into a shadowy world of secrecy and intrigue. Recruited by a mysterious supervisor, John is given a new assignment that involves identifying threats to national security. As his involvement with this clandestine duty intensifies, the line between his professional work and paranoid delusions begin to blur, leading to the emergence of a complex and challenging reality.