EDINBURGH FRINGE / Mary in helmet and gumboots banishes festival fatigue: The Dig;A Little Older; Serpent Kills; Brilliant traces; Grimm - The Telling ofthe Tale; Stalinland

IN THE final week of the festival, fringe fever gives way to fringe fatigue. Performers slump in cafes, rain-soaked posters flap in the wind, and the queue outside the Fringe office dwindles to a single luckless punter side-stepping a dozen leafleteers. Even the faces in the street are the same as the ones you've seen on stage. But, just when you start wondering if you will ever feel anything again, along comes a piece like The Dig to ambush your emotions.

Few pieces look less promising than this one-woman movement play about child abuse. But through a startling use of form and image, actress Karran Waterfield and director Ian Cameron, who co-devised the work, keep the audience intrigued through a cryptic sequence of events. The set consists of upturned brooms, billowing sheets and a stepladder. Mary, a former archaeologist, enters in yellow dress, pith helmet and gumboots and proceeds to dig into her private hell. A slight, impish figure, with a quick, nervous smile, she tells her traumatic story through a bizarre mixture of rituals, nursery rhymes, African songs and dance. Sometimes the images are explicit. When her father rapes her, she runs a red apple across her breasts and between her legs before choking and vomiting on the fruit. Later she literally ropes off her childhood and builds a prison around herself.

The Dig is more a theatrical poem than a play. It has an elusive, resonant quality that defies simplistic interpretation. I felt I'd been inside the mind of the young woman, which was exhilarating after seeing other social-issue plays which give you the sense of being trapped in a waiting-room listening to the drone of someone else's problem.

A happier childhood figured in John Binnie's A Little Older, winner of the Independent theatre award (it transfers to Hampstead Theatre from 26 October). This gentle story about a close friendship between Sandy, a young gay man (Stephen Docherty) and Isla (Mari Binnie), the daughter of a minister, takes place on a bare stage with only a wheelchair, some tinsel and a Christmas tree which lights up behind a curtain.

Isla has fractured her skull in a car crash and remembers nothing. Sandy visits her each day in hospital and prods, teases and pleads with her to remember their relationship. Mara Hinnie skilfully switches from hospital victim to roly-poly schoolgirl while the wry, self-mocking Stephen Docherty charts his own character's growing self-confidence through their reminiscences. Binnie's warm, observant play hints at darker, reckless reasons for the car crash. But these are only glimpsed at and there are no archaeologists on hand to dig deeper.

In the mid-Seventies, Charles Sobhraj was on Interpol's 10 Most Wanted list for multiple murder. According to a programme note for Serpent Kills, he is now in prison. The play reveals that he has made more money selling film rights to his life than he ever did from drug trafficking. The Canadian group One Yellow Rabbit present an energetic, sexy account of this amoral figure. It's a compelling enough tale, but the episodic structure of Blake Brooker's and Jim Millen's play only permits a series of bald exchanges and a ticking off of plot points in the master criminal's descent.

This kind of snapshot presentation of character and relationships was all too common on the Fringe this year. The strongest trend was towards movement, with many performers citing French teachers like Jacques LeCoq and Philippe Gaulier in their programmes. The biggest loss has been in the ability of writers to sustain long scenes: most tend to make a single point then go to blackout. The audience is denied the pleasure one gets from watching the chess moves in a relationship.

A welcome exception was Brilliant Traces by Cindy Lou Johnson. Rosannah (Kate Bennis) flees the altar in Arizona and pitches up in a wedding dress at the home of Henry (John Payne), a hermit in Alaska. Two fine performances held us through the intriguing developments in this unlikely pairing.

The sell-out success among the student plays was Edinburgh University's Grimm - The Telling of the Tales, a flamboyant production that stirred in, rather self-consciously, ideas about storytelling, the relationship of the Brothers Grimm, several folk tales and accounts of Napoleon at war. Toby Gough directed an inventive, spirited piece that overflowed with undigested ideas. The company now plan to take the production to Russia.

I much preferred the lean satire of Bristol University's Stalinland by David Greig. Sophisticated narrative techniques - concurrent scenes, flashbacks, transference of characters from one actor to another - were used in the story of a family reunion after the collapse of Communism. Images were spare and effective. The Communist sculptor clung on to the head from his smashed statue and, in one of the strongest scene-changes on the Fringe, a cascade of papers littered the stage after secret police files were ransacked. I wish they'd take this one to Russia.