Set in present-day London, a group of radical activists take over an energy company’s annual gala, taking 300 hostages to expose the corruption of the hosts. Their righteous cause is hijacked by an extremist within their own ranks, who is ready to kill everyone in the building to send his anarchic message to the world. It falls to a former soldier turned window cleaner, played by Ridley, to hang 50 stories from the outside of the building, to rescue those trapped inside, including her younger brother.