Father James is minding his own business in confession, when the man in the booth announces a major sin in advance of committing it - in just over a week he will murder Father James himself.

"Nothing to say to me, Father?" the unseen man asks. "Not right now, but I'm sure I'll think of something by Sunday week," is the wry reply.

This is the rum opening to John Michael McDonagh's follow-up to his scintillating debut, The Guard. Like that film, Calvary is a very dark comedy, though with a much more serious undercurrent, for its central character is an honourable man beset not just by his own melancholy, but by the most undeserving congregation any priest could have.

The priest (Brendan Gleeson) is given no reason for his imminent demise, other than the twisted logic that the best way to condemn the sexual misdemeanours of the Church is by killing one of its innocents; his nemesis is clearly a damaged, as well as dangerous soul.

James is given a week to prepare himself. Other men might pack their bags and flee town, or at least alert the police. But he stays put, mostly says nothing, continuing to work among his Irish coastal flock of drunks, wife-beaters, corrupt bankers, buffoons and ingrates, while trying to repair his relationship with his troubled daughter (Kelly Reilly).

Now, the priest has a pretty good idea who intends to kill him, leaving us to guess. Could it be the cold-hearted and sinister coroner (Aiden Gillen), the unctuous, possibly wife-beating barfly (Chris O'Dowd), the drunk and disgraced banker (Dylan Moran) whose flaunting of wealth alone deserves locking up, or the openly hostile local mechanic (Isaac De Bankolé)?

While the locals seem to uniformly resent the priest, outsiders are more appreciative, notably an ageing American writer (played by M Emmet Walsh) and a newly widowed Canadian (Marie-Josée Croze), whose holiday has ended in tragedy but who might offer the priest a way of avoiding his own.

Structured by the countdown towards the fateful Sunday, the story follows the priest as he tries to continue with business as usual, the tension increasing day by day. While James increasingly questions the validity of his life's work (he's accused of being "just a little too sharp for this parish") and, an alcoholic, struggles with the temptation to return to the bottle, he never questions his faith.

Calvary isn't as perfectly realised and nowhere near as much fun as The Guard. It's too schematic, the priest's moving to and fro between the characters/suspects too reminiscent of a rote TV detective series, McDonagh also tries too hard for eccentricity, forcing his gallows humour, and too many of the characters - notably Gillen's and Bankolé's - don't ring true.

But the writer-director builds his study of faith and integrity struggling in the face of day-to-day humanity well enough, shooting with an autumnal hue that suits his character's mood and dilemma. And, just as with The Guard, his ace card is Gleeson, whose towering performance as Father James carries us through both the film's bleakness and its missteps.

With his great, careworn face, the actor beautifully conveys the brewing emotions of a man who is at once idealistic and pragmatic, bullish and scared, stern yet deeply sad, clinging to God while despairing at all around him. The best thing that can be said about Calvary is that we really, really want this great character to make it beyond Sunday week.