Pilgrimage

 Somewhere in the southeastern coast of medieval Ireland, a tiny monastery keeps watch over a holy relic - the stone that was used to brain Saint Mathias more than a millennium prior (an event that's depicted in the film's prologue).

 Enter Frére Geraldus (Stanley Weber), a devout Cistercian monk who comes with a papal charter calling for a pilgrimage to bring the relic to the pope - Innocent III hopes the relic will help separate "the faithful from the faithless" for the next crusade, which is a really amusing detail given how the fourth crusade a few years before the events of this movie ended with the sacking of Constantinople and the pope's condemnation of the ensuing massacre.
 I have no idea if this was intended by scriptwriter Jamie Hannigan, but if so: hats off.

 A small problem: the relic seems to be cursed - both given the tales spun around it, and the visual language the film uses to depict it. Still, orders are orders, so a small group of monks is conscripted to take it to Rome. The group includes worldly, wise father figure Ciarán (John Lynch), young, idealistic Diarmuid (Tom Holland), and a mute layman in service to the monastery who's played by Jon Bernthal and thus predestined for badassery.

It's a matter of historic record that the only reason Jerusalem was lost was because they sent Jon Bernthal off.

 The pilgrimage is to take place through contested lands - at the time Ireland was being conquered by the Normans, so Geraldus asks the Baron de Merville (Eric Gordon) to help protect them from Gaelic warbands. The baron agrees, in exchange for absolution from his sins, and sends his son Raymond and a squad of knights to accompany them. It's quickly apparent, though that Raymond is up to no good, and soon the monks are running for their lives through hostile woods and moors and bogs. Good thing they have Jon Bernthal with them! By then it's established he has a crusader past, and it turns out he's pretty handy with a sword. And a shield. And... well, pretty much anything he gets his hands on.

 The action is brutal, gritty and pretty bloody - alas, mostly digital blood. The focus is more on the chases than in the fights, but what fights there are still have fairly complex choreographies; While they're not designed to show everything that's happening clearly, director Brendan Muldowney blocks things well and does a good job of keeping the flow of combat readable and engaging.
 The film is highly entertaining even when the monks aren't fearing for their lives. There's a lot of period detail to every scene, and while I'm sure that it's not all perfect, the fact that it's there is appreciated - I very much doubt that the French the English occupiers speak is period-accurate, for example, but, well, you've still got French-speaking Normans - who are at one point described as "grey foreigners" - invading Ireland for their king.

 Despite a fairly simple plot, it's a fairly complex, thorny movie that does right by the genre and even supports a little reading into as Diarmuid and Geraldus come to opposite interpretations of their travails. Add in some beautifully shot landscapes (cinematography: Tom Comerford), great music (Stephen McKeon), and a wealth of hilariously terrible haircuts, and we're cooking.