Identical twins separated at birth: One a prominent psychiatrist; the other a life long mental patient. When the doctor gets called to his brother's institution, fate intervenes and the brothers swap places.
Jack Harper (Tom Cruise) is one of the last few drone repairmen stationed on Earth. Part of a massive operation to extract vital resources after decades of war with a terrifying threat known as the Scavs, Jack’s mission is nearly complete.
Iconoclastic, take-no-prisoners cop John McClane, finds himself for the first time on foreign soil after traveling to Moscow to help his wayward son Jack - unaware that Jack is really a highly-trained CIA operative out to stop a nuclear weapons heist.