ENGLISH-LEBANESE playwright Claudine Toutoungi introduced herself to Stephen Joseph Theatre audiences this summer with Bit Part, a tale of sparring sisters that formed one of four parts of Screenplay, all short works on a cinematic theme in the McCarthy auditorium.

By then, the SJT already had commissioned Slipping, a darkly comic tale of eyes and lies that takes Toutoungi from bit part to the real deal in a claustrophobic two-hander in the mode of David Mamet's Oleanna, where friction, fact and and fiction clash and the truth is built on constantly shifting sands.

As chance would have it, Slipping slips into view at the same time that Harold Pinter's 1978 play Betrayal is being revived in Juliet Forster's York Theatre Royal production with its black-humoured inquest into sex, lies and deceit. Toutoungi more than holds her own against Pinter in the same turbulent territory, and the end-on McCarthy stage gives Slipping an intimacy, a proximity, that Betrayal lacks from being in the main house, rather than the Studio.

In Slipping you can see into the eyes. Or make that one eye in the case of Elena (Charlotte Harwood), who is soon to undergo life-changing surgery at the hands of ocularist Sean (Christopher Harper). Should you not know, an ocularist specialises in the fabrication and fitting of prosthetic eyes for those who have lost an eye through trauma or illness, and Toutoungi writes from experience, having undergone an eye removal because of glaucoma eight years ago.

Elena is complex, a tinderbox on the point of igniting. She wears an eye patch that is symbolic of a woman who masks the truth, a woman where you are never what is real and what is fake, much like the eyes. Sean, as it turns out, has plenty to hide too, but by then they have tumbled beyond the boundaries of the professional and his patient into a relationship, one where the more they discover, the less they understand each other. Sean is troubled as much by a spiralling coke habit as ethical quandaries; Elena ties herself in knots with her lying.

Toutoungi, meanwhile, is asking the bigger questions of how important is it to look "normal"; what passes as "normal" in this prosthetic age; how much can we trust ourselves to make the right decisions, be it in our health or relationships; all topped off by that age-old conundrum of whether business and pleasure can ever be mixed as successfully as the best cocktails.

She does so with wit and insight, while the SJT's new associate director, Henry Bell, directs with the same flair that he brought to Screenplay, aided by Paul Stear's Japanese-inspired video and sound projections that name and number each scene. Designer Lucy Weller's scene changes flow equally smoothly, her minimalism complemented by Tigger Johnson's pools of light.

Charlotte Harwood, the find of the SJT summer, reasserts that status, her Elena being alluring but dangerously on the edge, always fearing the mask will slip. She is both an eyeful and a handful for Harper's Sean, whose medical precision so contrasts with his recklessness elsewhere.

Ultimately, suggests Toutoungi, despite all the fakery, the truth will out. Keep your eyes on her; on the evidence of Slipping, she is definitely one to watch.

Slipping, Stephen Joseph Theatre, Scarborough, until Saturday, October 18. Box office: 01723 370541 or at sjt.uk.com