Look back on any relationship and it's a muddle. Passion tangles with heartbreak; good times with bad. First kisses and break-ups sit side-by-side so that, seen in a rear view mirror, love stories are their beginnings, middles and endings all at once. It's almost impossibly sad. Even love at first sight leads to some sort of last look. Every coming together engenders a split.

Fiona Doyle's two-hander is a mixed-up memory play. It shows us a relationship on shuffle. Where Harold Pinter puts love in reverse in Betrayal, Abigail skips back and forth, so that a couple miscarries before they first meet. They start breaking up before they've even begun. In the play's middle, the pair climb a mountain – a mark of their high-point, the moment they were most in love. It's all downhill from there. Doesn't every relationship have its peak?

Yet, it's the break-up that forms the play's backbone. A young woman and an older man – she in her twenties, he in his forties – met at an airport. Instead of heading home as planned, they make for a lush hotel. A few years later, maybe more, things have gone stale. He tries to end it. She refuses to leave. Love's not the only thing that dies that night.

Doyle gives us shards of their set-to: a raised bottle, broken glass, a headache, a collapse. Crucially, she doesn't show us exactly how they interrelate. We don't see the moment of impact – if, indeed, there is one. The scene skips a beat and it's up to us to fill in the gaps and put the pieces together. Was this manslaughter or a stroke? All we've got is background information; shards of their relationship, fragments of their characters. That's how stories – and, indeed, relationships or people – work. We never see them in full. There's more to her past than meets the eye; more than either we or her partner ever know. Max Dorey puts the play on a mountain of boxes; a set that speaks of moving out and memories, baggage and neatly packed narratives.

If it's smartly conceived, however, Abigail doesn't quite work. It's an early piece, and it shows. Doyle herself calls it a "‘nearly there' play." Her writing has flashes of brilliance, but just doesn't come together. The plot's not the right one - too rom-com at first, too soap opera to finish - and the text tries to do too much. Doyle dangles the idea, ambiguously, of abuse, and weaves in threads about history and travel. Talk of marble statues and equinox shadows suggest a sense that t'was ever thus: worldly older men with beautiful young women. The age difference instils the inevitably of death. One partner will always go first.

All of which weighs down Joshua McTaggart's production. In trying to pick everything up, his staging slows every scene. It dearly needs more speed, more nimbleness. In fact, it needs more everything: clarity, chemistry, drama and ease. Tia Bannon and Mark Rose are engaging actors, but they play every line as if musing on the way of the world; chewing over each thought, mulling every action and slowing a short, sharp play to a ponder.

Abigail runs at The Bunker until 4 February.