It’s hard to fault either the intention or the emotion behind the fact-based legal drama Just Mercy, a sturdy retelling of one of the influential lawyer and social justice activist Bryan Stevenson’s most enraging cases. It’s also damn near impossible to fault the performances of Michael B Jordan as Stevenson and Jamie Foxx as his client, both as good as they’ve ever been. But instead it’s director Destin Daniel Cretton, whose breakout indie Short Term 12 showed such promise, who can’t quite rise to the material or his performers, choosing anonymity over ferocity, making the dullest, safest decision at every turn. It’s not enough to topple the fascinating true story at his film’s centre but it does have a frustrating, flattening effect.

Stevenson, whose legend seems to rise with each year (most recently thanks to an HBO documentary), graduated from Harvard with a dream of making a difference. But unlike many of his peers, his idealism was focused on those at the very bottom of the food chain, death row inmates whom the system had deemed unworthy of due process. In the late 80s he started the Equal Justice Initiative to help right these wrongs and, in some cases, exonerate those who had been wrongly imprisoned.

In the film, he starts meeting prisoners and quickly discovers both the depth of the epidemic and his naivety over how much he can really achieve. When he hears about Walter “Johnny D” McMillan, a man who claims he’s been wrongfully accused of murder, he’s appalled and engaged in equal amounts, inserting himself into the case even if McMillan remains unsure. As he delves further and starts to construct enough evidence for a retrial, he finds the system unwilling to bend for the truth.

The film is far more successful in its portrayal of the good guys. As the woman who helped Stevenson set up his non-profit, Brie Larson is solid but it’s the two men at the film’s centre who truly steal our attention. Jordan’s movie star credentials have been affirmed time and time again at this stage but it remains a joy to see him lead and here he dials back his trademark charm for a more understated turn that remains as effective as anything we’ve seen him do.

Just Mercy is a straightforward, no-frills drama that does have an undeniably emotive effect. The finale in particular, although it perhaps goes one big speech too far, is incredibly moving and the film’s epilogue reminds you that Stevenson’s brave, important work is sadly not over.