For an intriguing barometer of our pressured times, one need look no further than the current repertoire of the National’s Cottesloe stage.

Both Happy Now?, by Lucinda Coxon, and this latest work from Simon Stephens, feature as protagonist a middle-aged, middle-class woman toying with the idea of opting out of her life. Yet while Happy Now?,which is likely to prove the more enduringly popular, veers in the end towards sitcom platitudes, Harper Regan is more unsettling.

It’s fascinating that both pieces have as a trigger the illness of a father, which brings the tightrope these working mothers customarily walk that bit closer to fraying. The first we learn of Harper (Lesley Sharp) is that she’d like a few days off work to return to Manchester to visit her Dad.

What she doesn’t say, but we soon understand, is that she’d actually like a few days off from her life, which comes complete with an inscrutable teenage daughter (excellent Jessica Raine), a husband who’s not working and money worries.

Request denied, Harper decides to go anyway, to go Awol. This, we sense, is a unique ripple of rebellion in a millpond of conformity and Sharp’s detached style of delivery, one turn of the dial away from naturalistic, beautifully suggests a woman surveying her existence from a great distance and finding it suddenly incomprehensible.

Director Marianne Elliott keeps everything moving fluidly on Hildegard Bechtler’s slick revolving design, although she can’t prevent a certain “So what?” quality creeping over the succession of excessively compartmentalised scenes, which tend to introduce characters who don’t crop up again.

Sharp, on stage throughout, takes us efficiently but unobtrusively along some of the corridors of Harper’s mind, although the door marked “problem husband” proves tough to open. Stephens might have helped her, and us, with a judicious shoulder shove here.

There’s one delightful pub-set episode that, before it culminates in unexpected violence, finally allows us the sight of Harper smiling. Wearing a long-coveted leather jacket, she can, for a few fleeting, flirting moments, behave irresponsibly. Sharp, squirming sinuously in her seat, revels in this change of dramatic temperature. Still, as we already know from Happy Now?, pleasure will have to be paid for, one way or another.

In rep until 9 August. Information: 020 7452 3000, www.nationaltheatre.org.uk.