Staying together for the sake of a child takes on additional weight in Eva O’Connor’s intense new play for Fishamble Theatre Company. In their mid-20s, Mo (Catriona Faint) and Réaltín (Lara McDonnell) initially seem like bickering young parents; “chosen family”, attending a therapy session, with the audience in the role of therapist. As the pair’s story spools back to their comical first meeting as new university students in Edinburgh, a portrait of an obsessive friendship emerges.

Playwright and actor O’Connor has written previously about compulsion, and here she vividly conveys the confusing mix of love, dependency, admiration and desire that can be poured into young women’s friendships: “the wild magnet pull of us,” Réaltín calls it. Initially it was the contrasts between the spiky, politicised Glaswegian, Mo, and the naive, middle-class Dubliner, Réaltín, that cemented their bond – captured in Faint and McDonnell’s committed, passionate performances.

As director Jim Culleton sensitively brings out, in tiny moments and gestures, Réaltín may be oblivious to the differences in their feelings; the distinction between loving and being “in love”. It hardly matters in their messy drinking and clubbing years, but post-college, when an emotionally lost Réaltín gets engaged to a wealthy Finnish man, the fallout is catastrophic.

Alternating between monologues for their competing memories, dance moves and bluntly humorous dialogue, the leisurely exposition of early scenes begins to tighten around the events of a single night, with tension underscored by Denis Clohessy’s sound design. At a party where sex, alcohol and jealousy slam together, the violent climax is all the more vivid for not being directly described.

Set designer Alyson Cummins’s simple raised platform rests on a layer of discarded bottles, books and junk, as if allowing us to see the detritus that has been swept under the carpet. O’Connor is very good at ensuring that we can’t look away.