"Doubt is not paralysis. Certainty is. Doubt keeps the doors and windows open. Belief is one room with no way out. Do not let others impose a polarity of response on you. You need not live a reactive life. Don't look to have life explained to you, presented to you. Live the life that emanates from your interior greatness. Be an overwhelming bounty of impressions, ideas, conflicting theories, and let the propellant behind all this be generosity. A giving." – 'Doubt' writer-director John Patrick Shanley.

This, then, was never going to be 'Sister Act 3'. Shanley's film adaptation of his own Pulitzer-winning play may have a minimalism his rambling above lacks, but it still does your head in. A complex, layered and at times frustratingly ambiguous treatise on human behaviour, moral dilemmas and the impact of sweeping societal changes, it ticks all the big boxes: faith, religion, race, abuse, civil rights, and morality. Don't let the deceptively simple story fool you.

Set in a Catholic school in the Bronx circa 1964, 'Doubt' ostensibly details a battle of wills between the sanctimonious principal, Sister Aloysius Beauvier, and the charismatic Father Flynn. She's a staunch traditionalist who rules by fear and discipline ("The dragon is hungry," he quips at one point as she publicly humiliates another pupil), he's a progressive thinker keen to relax the church's fire and brimstone approach.

They tolerate each other at best. So when the eager to please Sister James shares with her fearsome superior suspicions about the priest's interaction with one of the boys, Sister Aloysius launches a vigorous personal crusade to uncover the truth — and drive the demon out of her school.

As the relentless moral crusader, Meryl Streep is genuinely intimidating, driven by her singular vision of what is right. As the target of her witch hunt Philip Seymour Hoffman performs a fine balancing act. And Amy Adams is superb as the impressionable young nun, representing the audience as her allegiance shifts from one side to the other — thanks to Shanley turning his established stereotypes on their head.

Flyn's charm, humanity and smiling round face may mask a serious character flaw. For all her resistance to the progress represented by ballpoint pens and secular Christmas songs like 'Frosty The Snowman', the fiercely intelligent Aloysius is clearly doing what she thinks is best. It's even understandable — until her actions threaten innocent parties. And even the small but seismic part of Mrs Miller (Viola Davis) is fraught with shocking contradictions that bring into question any preconceptions about responsible parenting.

He may not actually answer any of these questions he asks, but Shanley succeeds in creating a sense of doubt that lingers even after the unintentionally less-than-shocking denouement.