When 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 the disaster from escalating into an even greater catastrophe.