In modern-day London, a group of radical activists take over an energy company's annual gala and take 300 hostages in order to expose the hosts' corruption. Their just cause is hijacked by an extremist in their ranks, willing to kill everyone in the building to send his anarchic message to the world. It follows a former soldier turned window cleaner (played by Daisy Ridley) who clings on 50 stories above a building to save those trapped inside, including her younger brother.