We know what we've seen – Alice was motionless, face down in the water for a long time before her cough and splutter of an awakening – but the first 10 minutes of This is Living are satisfyingly ambiguous nonetheless. Perhaps, as Alice insists, she and Michael have just ended up in this bleak place after a wild night that neither of them can remember.

Eventually however she, and we, have to face facts. Alice is dead – drowned saving their little daughter from the same fate – and this whole conversation is taking place in Michael's head. It's testament to the skill of playwright and director Liam Borrett that this scenario comes across as neither maudlin nor clichéd.

Lighting designer Jackie Shemesh jolts us back to the moment the couple meet, offering us a vision of happier times. It's the first of many switches, but the device never loses its power, thanks to Tamla Kari and Michael Socha's skill in navigating the emotionally ragged transition between the two states.

Socha in particular is excellent in this regard, his whole demeanor lightening each time he's able to lose himself in the past: their first date, their wedding night, the cruelty of a miscarriage and the bittersweet discussion about trying again. Kari shows similarly impressive range, but it's in her moments of devastated stillness, rather than when she is raging, that the actor is at her strongest.

It is Kari and Socha's expert handling of the comedy in Borrett's script that really makes this play though. The writer does well to capture the very funny moments of awkwardness of that time in a relationship before two people are quite comfortable with each other and Kari and Socha have some killer lines, the silliness coming out of their mouths a balm for the grimness of the scenario lurking in the background.

Sarah Beaton's design, a shallow, tarpaulin-lined trough of water in which Kari and Socha spend almost all their time on stage, while not exactly aesthetically pleasing, is dramatically effective, offering a constant reminder of Alice's watery demise. Time passes for Michael and Alice in the strange dream place where they meet each night, her funeral getting ever closer, but her dripping clothes and clammy skin give the impression of a corpse freshly pulled up onto the bank in every new scene.

The play loses momentum in the second half, becoming mired in the purely grim for a time before finding its way again in an ending that shouldn't feel happy but somehow manages to do so. The final scene is unnecessary – encumbered by props where the rest of the play is sleek and minimal, it feels like it's there purely to show off a clever bit of set design – but it does no great harm to the whole. This Is Living is Borrett's debut play, and it's an assured and ambitious start.

Running time: Two hours (including interval)

This is Living runs at the Trafalgar Studios until 11 June 2016.