Set in present-day London, a group of radical activists take over an energy company’s annual party and take 300 hostages to expose the corruption of their masters. Their just cause is hijacked by an extremist within their ranks, ready to kill everyone in the building to send his message of anarchy to the world. It falls to a former soldier turned window cleaner, played by Daisey Ridley, who hangs herself 50 stories off the outside of the building to save those trapped inside, including her younger brother.