Not whodunnit, but whether he dunnit; THEATRE

AT THE END of Anna Weiss, a searching new play at the Traverse by Scottish playwright Mike Cullen, you still don't know whether the father did or whether he didn't. It may seem odd in a play that achieves a remorseless simplicity that the issue of sexual abuse remains this obscure. But then that may just be Cullen's point.

In Vicky Featherstone's enthralling, spartan production a few packing cases are spaced round the stage: a tidy metaphor for a hidden past that is about to get unpacked. Anna and Lynn are moving house. But first, Lynn's father, David, is turning up. Lynn wants to read him something she has written. It's a record of how he has abused her. All he has to do is listen and not interrupt.

We think the daughter's confession will lead to the father's. Before Lynn can speak to him, Anna, the psychiatrist figure who has helped Lynn retrieve these memories, tells David that he must accept whatever Lynn says. To deny it would only add to the harm he has done (she may kill herself). The problem for David - other than his daughter's suicide threat and fierce hatred - is that he doesn't think he did anything. He has no memory of it.

It would be hard to think of Cullen dramatising a more treacherous, slippery subject than False Memory Syndrome. It cries out for the judicious treatment of documentary drama: a level, reasoning, investigative tone. We don't get it here. Cullen's subject instead is the horror that stems from the confusion. The events of the past are overtaken by the events of the present. Anna Weiss has the kind of taught questioning dynamic that drives Pinter's Ashes to Ashes or Mamet's Oleanna. We see the power people exert (Anna over Lynn, Lynn over David) once these accusations surface.

Featherstone directs this fraught debate with rigorous assurance: Iona Carbarns plays the young woman whose memories lead us into a solipsistic nightmare (she says she believes it, so as far as she's concerned, it's true), Anne Marie Timoney is the severely supportive Anna who shatteringly learns more about herself, and John Stahl is the bulky, anguished father who early on attracts our disgust. All are excellent.

In Fool House Joff Chafer and Toby Wilsher have written and directed a black farce that has the technical ambition of an Ayckbourn. The house is on four levels in a street in present-day Amsterdam. When the residents enter the house they either go up the stairs, or down them, or remain on the ground level. Whichever way, they end up occupying the same room. Despite the constant nosiness of the landlady (Karina Garnett), no one notices that the man in the basement has committed suicide. His body is discovered - a whacky development, this - by 17th-century sailors who died in a shipwreck and who climb out of the sofa from the earth below where they have been preserved by the peat.

So far, so ambitious: the other key detail about Fool House is that this is a Trestle Theatre Company production. All the characters have masks, large expressive loveable ones (doleful, shy or smiley) created by Chafer and Wilsher. These mute figures give the farce a surprising comic dignity: there's an endearing truth in each of them having one basic expression. As so often with Trestle, the characters are nicely observed, with a quirky, unforced humour. If you hadn't seen the cast list you'd be amazed at the end of this ingenious saga when only four actors come out and take a bow.

In Steven Berkoff's Massage, the actor-director gets into drag. It's an impressive sight. He plays Mum, who loyally cooks her husband's breakfast, then totters off to run a massage parlour, or, as Berkoff inimitably puts it: "this darkened hell-hole of the pumping wrist". Berkoff's Mum is a busty, bustlingly generous figure, flicking her red hair away from her heavily made-up eyes, mincing round the parlour, before slapping oil across her customer's body and providing a variety of "relief". Across 10 minutes, it's a laugh. Across 90, it becomes a drag.

Massage grows into a series of repetive monologues when it ought to have stayed as a sketch, introducing another comic cameo to the Berkoff family album. In Massage, the author hasn't enough curiosity in Mum or Dad to sustain our interest. He prefers to restate points in half a dozen ways. Here's Dad - well-played with a Stan Laurel-ish innocence by Barry Philips - when he discovers his wife's a whore: "my darling wife has flogged her rose/my flower/my ornament of joy/my sceptre/my own doughnut ... my little mouse/my winking puss". And so on. You could be trapped in Roget's Thesaurus.

For energetic physical theatre, far better to see Disco Pigs, a new Irish play by Enda Walsh, (which transfers to the Bush in September). Two 17- year-olds, who've known each other from birth, go out for a night on the town. As Pig and Runt, a self-styled Bonnie and Clyde couple, Gillian Murphy and Eileen Walsh take hold of the Traverse stage as if it's a boxing ring or a dance floor. Together, they are a tour de force. Whether they're watching Baywatch, getting into fights or joining a Sinn Fein karaoke night, they do in an uncompromisingly private rhythmic language. It marks out Disco Pigs - directed by Pat Kiernan, and with a pulsating "soundscape" by Cormac O'Connor - for the unassailable sense of its own identity.

One-person shows tend to hinge on what you think of the one person. In Elephant Wake by Jonathan Christenson and Joey Tremblay at the Hill Street Theatre, a nerd pops up from behind a long table, with a small plastic elephant's trunk on his nose. He has a moist face, a grubby yellow sweater and a nervous snigger. Every other sentence ends with "eh?" The heart doesn't leap at the thought of the next 80 minutes. Elephant Wake does offer a peculiarly original insight into the Metis, an isolated French- Canadian community, caught between anglophone Canada and America. The staging is as eccentric as Jean-Claude (Joey Tremblay) who shows us models of his family tree, done by lining up bottles, and how to make glue from papier mache (mix flour with water). Unfortunately the show's distinctive regional flavour never overcame my early prejudice against one of its inhabitants.

Art, Sex and Politics is a 50-minute cabaret performance of German songs by Josephine Allendorf, accompanied by violin and piano. Allendorf suits the grave, biting numbers (lyrics by Brecht) better than the coquettish ones, but this show is just the sort of accomplished unexpected pleasure - that includes songs not performed since the Weimar Republic - you hope to stumble across towards midnight at a Festival.

'Anna Weiss': Traverse (0131 228 1404); 'Fool House': Pleasance (0131 556 6550); 'Massage': Assembly Rooms (0131 226 2428); 'Disco Pigs': Traverse;'Elephant Wake': Hill Street (0131 226 6522); 'Art, Sex and Politics': Roman Eagle (0131 225 7226).