New York-based romantic comedies may be less popular in the cinema and on stage than they once were, but they are so plentiful that each needs to be distinctive to succeed. At first, Adam Gwon’s Ordinary Days seems to revel in its titular ordinariness. The cast comprises solely of a struggling artist, a similarly struggling grad student and a pair of young lovers taking the plunge to move in together.

And yet from the first song, Gwon’s quirky take on life begins to shine through. The central couple (Alistair Frederick and Kirby Hughes) sing individually about their feelings about the speed at which their relationship is growing, with Frederick’s Jason seemingly oblivious to the hesitancy Claire (Hughes) is showing. As their relationship progresses, the fault lines deepen until, in the duet ‘Fine’, the couple’s row is concluded by Jason proposing to Claire, a question that seems to take both lovers by surprise.

Under the directorial gaze of Jen Coles, Frederick and Hughes play the couple as refreshingly believable pair. This pair are ordinary, average, usual – but yet they are still interesting and compelling to watch. Gwon’s script and score is a big part of that, to be sure, but only a portion of the show’s success can be down to the composer alone.

Parallel to Jason and Claire’s story, Nora Perone’s struggling student Deb, whose dissertation on Virginia Woolf is threatened when she loses her book full of notes, is less obviously appealing. Perone manages to make Deb a spiky, forthright individual who unexpectedly finds friendship with Neil Cameron’s perpetually perky struggling artist Warren. To a certain extent, these characters exist as comic offsets to the musical’s core romance. And certainly Perone and Cameron play to that element very well. But their relationship also forms a rarely seen element of Manhattan romcoms, one that recognises how forming friendships in big cities can be as hard as finding love.

The show is slight in time, running at 70-odd minutes without interval. But within that short space of time are some classic numbers that have found their way into many musical theatre performers’ cabaret repertoire. The duet ‘Fine’, detailing the passive-aggressive fighting of Jason and Claire as they struggle to get to a party on time, is a masterclass in writing about everything other than the relationship between the couple – and Frederick and Hughes play it perfectly.

But the key song, thematically, structurally and emotionally, is all Hughes’s. In ‘I’ll Be Here’, her character Claire details the reasons she has been so emotionally distant from Jason, why she has reacted the way that she has to several situations, in a piece of storytelling that is funny, touching and, in its placement of a particular place and time in New York’s history, heartbreakingly poignant. The sparse fringe staging at London Theatre Workshop – in front of a painted Manhattan skyline by Samantha Cates and accompanied by Rowland Braché – allows Kirby Hughes to deliver a performance of one of modern musical theatre’s greatest ballads that will stick in the memory.

Ordinary Days plays at London Theatre Workshop until June 17, and during the Edinburgh Festival Fringe at C Venues August 2-28.