In modern-day London, a group of radical activists hijack an energy company's annual gala and take 300 hostages to expose the corruption of the hosts. 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 and current window cleaner, played by Daisy Ridley, who dangles 50 stories above the building to save those trapped inside, including her younger brother.