Though neither he nor Sean Harris should ever be described as particularly versatile actors, Jack O'Connell really does work well in this brutal and gritty drama. He ("Hook") is a soldier who becomes separated from his unit after a riot on the streets of Belfast sees his colleague shot in the head, and him pursued - unarmed - through an hostile urban terrain. He's been injured, is disorientated and is under no illusion that there are men chasing him from the Provisionals who want to kill him. What now ensues is a really tensely directed and sparingly written depiction of just how the…