The police have been called to these offices to arrest a burglar (Sid James), but when they get there they find the loot being replaced by a clergyman who calls himself Father Ignatius Brown (Alec Guinness), so they arrest him instead. On taking him to the station, he acts bemused that he should be brought here when he believed he was doing good works, but is escorted to the cells anyway while the sergeant tries to secure some kind of identification on him. The more he finds out, the more baffled he is: Father Brown is indeed a priest, and he does indeed got to great lengths to save souls...
This was based on the first of G.K. Chesterton's Father Brown stories, The Blue Cross, which had been filmed before in the thirties, but this was regarded as the definitive version in spite of its updating to the then-contemporary fifties, and generally the best reading of the fictional detective. Chesterton was a hugely popular author in his day, and if he's been largely forgotten now his Father Brown invention endures to an extent thanks to regular revivals in adaptations on both large and small screens, and the original stories have never been out of print, much like Chesterton's friendly rival Sir Arthur Conan Doyle's Sherlock Holmes stories, if nowhere near as high profile.
What the writer liked to do with these tales was use them to deliver the dilemmas of morality and reason which occupied him, so while they could be applied to comedy as they were here, the essential questioning nature of their plotting was not to be ignored, and certainly was not here by director Robert Hamer. He was by all accounts a deeply anguished man who sought solace in alcohol, leaving his career regarded as one which not often enough hit the heights of which he was capable. In drama, his work had a bleakness, but his most famous work was Kind Hearts and Coronets, a no less grim yarn dressed up with wit and flair so that Hamer's concerns for humanity were more palatable.
Although on the surface Father Brown was a far lighter work, its themes were no less serious, wrapped up with forgiveness and redemption as its worries where the sleuth attempts to save the soul of a master criminal who is seeking to steal the priceless cross that hangs in his church. Not helping in the priest's endeavour is this criminal, Gustave Flambeau (Peter Finch), is a master of disguise and the police may know he has "liberated" a collection of valuable objects, but still have no idea what he looks like. You may well know what Peter Finch looks like which elminates that part of the mystery, but nevertheless this didn't spoil things too much as Flambeau is easy enough to spot, even before he makes the slip alerting Father Brown that his travelling companion is not on the level.
Early on the holy man delivers a sermon making the point that everyone is capable of terrible evil, no matter how decent they think they are, which makes us all equal in the eyes of God, and for that matter the law. What this says about being innocent until proven guilty is up to you, but just as Father Brown tells us how bad we can be given the wrong circumstances, the opposite is also true and what he banks on in pursuing his quarry: it's not so much bringing them to justice for the police he's obsessed with, as he is saving their souls. This tied into Chesterton's rationalism, but also his, to some views, contradictory belief in a higher, supernatural power looking down on us, which some may find hard to reconcile, but this paradox was what lent his writings their particular texture. The moralism of this film does bring things to a happy ending, and Hamer managed a lightness of touch to keep Guinness's at times too cute interpretation balanced with the more serious aspects to offer food for thought if wanted. If not, you had a neat little comedy thriller anyway. Music by Georges Auric.