Ken Rudolph’s review published on Letterboxd :
Belfast, Northern Ireland was the most evil place on earth in 1971 (it had lots of competition from other "B" cities that year: Bucharest, Belgrade, Beirut.) However the factional civil war in Belfast between the Catholics (IRA, Provos) and the Protestants (including the British army) was tearing the fabric of civilization apart in that beleaguered city. This film is the story of a British private soldier (another extraordinary performance by young Jack O'Connell) who is separated from his mates after a lethal confrontation at the border between the two factions and viciously hunted down by both sides for different reasons.
The film re-creates the time and place with frightening accuracy (even if it actually was shot in England.) It ratchets up the tension to an almost unbearable degree. My only problem with the film (other than occasional difficulty understanding the accented dialog), was that I was never quite certain who was on which side, since treachery seemed to be everywhere and loyalties were confused.