In modern-day London, a group of radical activists take over an energy company’s annual gala, seizing 300 hostages in order to expose the hosts’ corruption. Their righteous cause is hijacked by an extremist in their ranks, who is willing to murder everyone in the building to send his anarchic message to the world. It falls to a former soldier turned window cleaner, played by Daisey Ridley, who is dangling from the 50th floor outside a building, to save those trapped inside, including her younger brother.