Unflinchingly written and directed by Austin, Texas-based filmmaker Ric Roman Waugh, it’s too unnerving to recommend to the squeamish, but for anyone curious enough to find out what really happens to turn decent people into savages in the bedlam of the American prison system, this is one for the must-see list.

Shot Caller may cover little new ground but navigates familiar terrain with considerable skill.

Shot Caller is Coster-Waldau’s show, and he’s up to the task.

It’s a genre movie, to be sure, but there’s an impressive sense of authenticity — in the language, the locations and the overall texture —that goes a long way to sell the scenario.

The whole film rests on the increasingly prison-ink tatted shoulders of Coster-Waldau, Game of Thrones’ Jaime Lannister, who brings his A – as in ass-kicking – game to Waugh’s film.