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