Theatre, however powerful, often struggles to translate to film.

Based on the play Blackbird, Una’s eponymous twenty-something (Rooney Mara) finally tracks down the man who abused her as a child (Ben Mendelsohn), too promising he would run away with her. Surprising Ray at his work after fifteen years, the film unspools largely as a duologue between the two formidable performers.

The content duly discomforting and at times confronting, though not always for reasons that would typically be expected as the life Ray built for himself post-prison is soon threatened by Una’s appearance, together the performers are transfixing from the moment their pained reunion takes place. With both balancing the most and least sympathetic aspects of each character and roundly challenging the preconceptions any may reasonably bring to this film having read the synopsis, the depiction of Una’s harrowing drive to encounter the man who so irrevocably changed her life is only matched by Mendelsohn’s treatment of the now secluded predator who has to reckon with the adult Una and Ray’s long-held desires.

The Australian performer ably tackling the unglamorous role, never pivoting to either theatrical extreme of what one could expect from the depiction of a child-abuser who has since sought to define himself as a loving family man, Mendelsohn is joined by his Rogue One co-star Riz Ahmed, among a few additions to the cast never on screen long enough to carve out a space in the film not already overwhelmed by the two leads.

Their performances done little justice at times by the darkly lit warehouse in which much of the action takes place, Una is at its most involving whenever Mara and Mendelsohn are permitted a rampant, no holds barred exchange, the tension hampered at times by the awkward additions of a workplace drama and jumps between unnamed locations where the pair ruminate on their previous encounters.

Rising and falling on the considerable abilities of its flagship cast, Una could have been that much better for allowing the two rightly celebrated performers to just let loose and let the camera, without the need for so many jarring interruptions, capture it all.

Una is screening at the Sydney Film Festival