While You Lie/The Girl in the Yellow Dress, Traverse Theatre, Edinburgh (2/5, 3/5)

Punishing times at the Traverse this August – unless, that is, you happen to enjoy being locked in a basement in close proximity to warring couples, sadomasochistic power play and masturbating males. While You Lie is the theatre's much-trumpeted "flagship production" of the season. Bearing the burden of this hype is Sam Holcroft, a 27-year-old playwright who came to prominence with her debut, Cockroach, in 2008.

It all starts promisingly – we're in the flat of a gorgeous twenty-something couple getting ready for a night out. Edward is besotted with Ana, his perfectly formed Eastern European girlfriend, but Ana has more hang-ups than a cloakroom and their relationship is soon dashed on the rocks of her neuroses.

In search of security – and possible promotion – she offers herself up to her monstrous boss, who carries the master-slave dynamic through to the bedroom with a little too much enthusiasm. Meanwhile, his relentlessly unglamorous, heavily pregnant wife clucks about at home. When Edward discovers Ana's affair, the battle-lines between the four are drawn. Holcroft over-eggs this intriguing pudding, though, with a bizarre plastic-surgeon figure who keeps cropping up to offer each an alternative fantasy life.

It's not clear what Holcroft is trying to say – we're obsessed with appearances, body fascism is evil, all men are animals, all women are domestic drudges or whores (no Madonnas?) – or maybe all of the above. And if the mixed messages weren't hysterical enough, it all descends into farce at a climactic barbecue involving a picnic-table caesarean and a roast chicken.

Holcroft clearly has talent to burn and the cast is excellent, but there's a woeful lack of control here. Shame.

The Girl in the Yellow Dress is a quieter piece, though the underlying ideas are no less dramatic or disturbing. It's a thrilling two-hander pitting an enigmatic English teacher, Celia, against her French-Congolese pupil, Pierre. Over a set of lessons in Celia's Parisian flat, the pair engage in a sexual/linguistic dance, which mines the gaps between speaking a language and expressing oneself.

Craig Higginson's script is tricksy and compelling, testing the skewed relationships between pupil and teacher, black and white, stalker and prey, lover and loved. The final slide into darker areas lacks restraint, but the twisted chemistry between the alternately brittle and frisky Celia (excellent Marianne Oldham) and her inscrutable student (engaging Nat Ramabulana) is palpable.

To 29 August (0131 228 1404)