There is one truly sublime moment in Just Mercy, near the beginning. Bryan Stevenson (Michael B. Jordan), a legal intern on the verge of taking the bar, has been sent to meet with Henry (J. Alphonse Nicholson), a young man of about Bryan's age on death row, to give him the news that there is no news to be given at this time. Bryan delivers this information in a crisp, professional way, and Henry - assuming that every day will bring with it the assignment of his execution date - reacts with an explosion of relief that he has at least awhile, long enough to tell his family that it's okay to come visit him. And he embraces Bryan, and the look on Jordan's face is the most perfect little bit of acting: he's absolutely shocked that something he views as a banal chore could so profoundly affect another human being, and his face completely falls slack. And then - you can actually watch Jordan re-activating his muscles - Bryan finds himself moved to his soul by the realisation of what's happening in this place, to a person who's so very like him in so many ways. This moment, we're to understand, was transformative for Bryan, pushing him to become a crusading lawyer working against the death penalty, and Jordan lets us in to see that transformation right before our eyes. And for this sequence, I was convinced: I had it all wrong about Just Mercy. It wasn't just some cruddy Oscarbait, designed to provide a bland, re-affirming moral lesson for a middle-class liberal audience of middlebrow liberal cinema. It had warmth and humanity to drive that lesson with art and grace.

Spoiler alert: I didn't have it all wrong. Just Mercy is at times some pretty cruddy Oscarbait indeed, and its relationship to its middle-class liberal audience verges on the pornographic, especially in one sequence that I don't really suppose I ought to describe, for fear of heading into spoiler territory. Let us say only that it suspects its audience is there to watch African-American men suffering nobly, and it does everything in its power to fulfill that desire in a crass, frankly offensive depiction of an execution: I am sure that if pressed, the filmmakers, led by director and co-writer Destin Daniel Cretton, would have it that the point is to sugar-coat nothing, and to provide us with a blunt encounter with the cruelty of the prison system and make us feel outraged at a country that still allows this kind of thing to happen. In practice, it just feels, well, pornographic, a titillating display of violence to make sure we get to work up a good lather and exercise our righteousness and all the other things, and I frankly despised it and the film that included it.

But that's one part of the movie. In truth, Just Mercy is routinely a much better film than I was expecting, even if it's also routinely exactly the sort of boilerplate Oscar season message movie that I greatly feared. And not all of that falls to Jordan's performance (he never gives up on the movie, even when it gives up on him and shovels him some pretty overwritten legal monologues), nor even necessarily to the acting at all. For a few pretty substantial chunks of its middle, Just Mercy forgets that it's a tedious message movie and instead becomes a legal procedural thriller, and this is something it turns out to be quite good at.

The film's proper story picks up with Bryan a few years after that transformative moment: he's arrived in Montgomery, Alabama, bringing along with him a nonprofit legal group that's more dream than actual organisation, the Equal Justice Initiative. The goal of the EJI - which at this point consists of nothing but Bryan and Eva Ansley (Brie Larson) - is to offer free, high-quality legal advice to anybody who seems to have received an unfair trial, especially persons who've been sentenced to death. And in Alabama, that population consists largely of poor African-American men, who view the educated, upper-middle-class Bryan with a healthy amount of dubious suspicion, until he manages to start helping budge their various appeals through the intractable legal system. The case that the movie foregrounds is that of Walter "Johnny D." McMillian (Jamie Foxx), a man whose innocence could not be more flagrantly obvious, which frankly feels like the movie's cheating a little bit; if it were really trying to be anti-death penalty, perchance an actual guilty man, or at least one whose culpability is a little bit ambiguous, would have been more dramatically charged. But this is a crowd-pleaser, not a philosophical tract, and it's also based on a true story, so I should stop grousing, even though the film kind of openly draws attention to the fact that it's cheating.

Anyway, that's a whole lot of angles for a message movie, on top of the "based on a true story" angle, which means of course several title cards at the end telling us how all of this played out in the most morally uplifting way possible. And none of this is the part of Just Mercy that's good. In fact, most of this sucks, primarily because of how minutely didactic Cretton & Andrew Lanham's writing is. This is not a movie that believes its audience can think. Every solitary piece of significant exposition is repeated, sometimes twice - Larson's character exists almost solely to reiterate things that we already know, and to do it in a twangy Southern accent that's so awful it almost turns back around to endearing - and themes are laid out in language so plain and artless that it's a little amazing Cretton can avoid the urge to have the actors stare directly into the lens while stating them. That is to say, we're a long way from the humane sensitivity of Short Term 12, the lovely 2013 feature that put Cretton and Larson on the radar of anyone lucky enough to spot the delicate storytelling and character-building of that underseen marvel. Just Mercy is as about delicate as train derailment.

But, it has one thing going for it. Given how much it wants to be a Serious Message Movie About Important Issues, Just Mercy spends a really surprising amount of time ignoring the social ramifications of what it's up to altogether, abandoning its leering emotional appeals, and letting its characters down off their soapboxes, focusing instead on the nuts-and-bolts work of assembling a legal appeal. This is where the Cretton of old actually wakes up for a bit: there's nothing romantic or glamorous about Bryan's job, just a lot of schlepping from one bureaucrat to another, shuffling through page after page of records in order to find something that isn't useful but points to something else that might be, and dealing with the preening passive-aggressive condescension of cops, judges, and district attorneys for whom the phrase "defense attorney" is only slightly less morally appalling than "cannibal pedophile". Jordan is good enough at simply inhabiting Bryan's body, walk, and silent facial reactions to make all of this procedural grinding feel anchored in character, so it's never as boring as I'm probably making it sound. Simply put, the parts of Just Mercy that aren't pandering Oscarbaity claptrap with a showily mournful Jamie Foxx and lots of big emotional splats are a genuinely gripping and at times moving story about how much tedious work it is to do the right thing. It's frustrating, sometimes thrilling, and a tribute to the dogged conviction of a damn good lawyer; if the rest of Just Mercy was as unsentimental and pragmatic, we might even have ourselves a real movie here.