Set in present-day London, a group of radical activists take over an energy company's annual gala, seizing 300 hostages in order to expose the corruption of the hosts. Their just cause is hijacked by an extremist within their ranks who is ready to murder everyone in the building to send his anarchic message to the world. It falls to an ex-soldier turned window cleaner, played by Daisey Ridley, suspended 50 stories up on the outside of the building, to save those trapped inside, including her younger brother.