How do you take an award-winning, one-woman play and turn it into a movie of equal calibre? Spoiler: you don’t.

Adapted from Susan Miller’s play of the same name, Prima Facie is the story of Tessa, a hotshot criminal defence lawyer who’s making a name for herself in court largely by taking on numerous sex offence cases. She’s unperturbed at the notion of defending potential rapists – she’s simply offering her legal services, providing the defence – after all, everyone’s entitled to it.

All this takes a sudden turn when Tessa is raped by a colleague and thus finds herself on the other side of the courtroom, subject to all the legal tricks and tactics that she herself so effectively employed.

Thematically, the story is important, shedding light on the prevalence of sexual assault, the unique challenges such cases face, and the difficulties of bringing perpetrators to justice. But, as intriguing as the plot is, it was the dazzling central performance (most notably, Jodie Comer) that drew audiences to the theatre night after night for this two-hour monologue.

Therefore, the decision to adapt Prima Facie into a more traditional film is one filled with risk and, unfortunately, it doesn’t pay off.

Cynthia Erivo plays Tessa and now shares the screen with castmates, an immediate departure from the play’s original format. Erivo is perfectly adequate in the role but it’s nothing to blow anyone away. Gone are the monologues (aside from some intermittent voice-overs that director Susanna White needed to either commit to or scrap entirely) which honestly, leaves Erivo with very little to do. Her strongest moments aren’t in the courtroom or dealing with the aftermath of her assault but in the scenes she shares with Noma Dumezweni and Toheeb Jimoh who play Tessa’s mother and brother respectively. Here we see Tessa with her guard down, slightly code-switching to reflect her more humble upbringing, and it’s where Erivo excels most.

Daniel Ings plays Julian, Tessa’s would-be boyfriend and assaulter. No offence to Ings but we know Julian is trouble from the moment he first appears on screen. He’s slimy, charming and performatively vulnerable in a way that’s typical to the London legal scene (he’s this close to being a ‘finance bro’). Ings is good at this, but we’ve seen it before and this signposted arsehole persona takes away from the shock factor of Tessa being raped by someone she trusted and cared for.

In fact, the sheer ‘obviousness’ of Julian as our villain is reflected elsewhere in the film. Everything is so predictable – regardless of whether you’ve seen the play – and bland. Watching, you just know what’s going to happen. There are no twists or turns, no change of pace, no surprises. The movie is so procedural that by the time we reach the courtroom scenes, we are essentially watching characters recount what we have just seen. There’s a very ‘BBC drama’ feel to the whole thing, not something you’d go to watch at the cinema.

Despite an Oscar-nominated lead actress, dazzling source material and a beautiful London backdrop, Prima Facie has been reduced to a bland courtroom drama that doesn’t do its subject matter justice.

Prima Facie is in UK cinemas from 13 November.