hen an explosion seals off a commuter tunnel, the survivors are faced with toxic fumes, fires and the impending collapse of the tunnel. Their only hope lies in the hands of Kit Latura (Stallone), a former Emergency Medical Services chief who is haunted by a tragic past. As the walls cave in and the tunnel fills up with water, Latura risks his own life to save others and prevent further disaster.

Overview from themoviedb.org