A car slowly winds its way to the rooftop of a dimly lit multi-storey car park, where the blonde driver steps out into the open air. The mood is sombre and eerie, as she gazes over a nocturnal cityscape. Only one thought is on her mind: to kill herself. This is the evocative, mysterious opening of Colum Eastwood’s Black Medicine, which would done a lot better to have maintained this scene’s exquisite noirish tone. Instead, a weakly predictable script means it quickly falls apart.

The woman is Jo (Antonia Campbell-Hughes), a freelance medical contractor who carries out shady medical procedures on behalf of crime bosses. Her suicide attempt is abandoned after a phone call that calls her to one such illegal operation. Though stoic in the face of mobsters, Jo’s personal life is falling apart, estranged as she is from her husband after their daughter’s death. For years an emotionless cog in the machine, she turns rebellious when she decides to shelter Áine (Amybeth McNulty), a teenage runaway who is in hiding from Jo’s boss Bernadette (Orla Brady). Áine has naively agreed to sell a kidney to Bernadette, not knowing that Bernadette actually wants her heart for a transplant operation that would save her dying daughter. No longer numb from her past traumas, Jo races to save Áine and to relocate her own humanity.

As Black Medicine stumbles its way through heavy-handed dialogue and contrived plot points, it squanders the brilliance of Campbell-Hughes, who gives an amazing performance. Underneath the stoicism, pain is subtly etched into her features and gestures; as Jo conducts these illegal surgeries, Campbell-Hughes gets across not only the character’s efficiency but also the fact that this is all a coping mechanism. Brady is equally great, alternating between heartbreaking maternal anxiety and cold-blooded cruelty. It’s a real shame that the cat-and-mouse dynamic between the pair is completely wasted in this bumbling mess.

• Black Medicine is released on 12 July on digital platforms.