Suzanne Robertson still remembers finding Lifeboat's musical director down the back of the piano one lunchtime, rubbing the strings with a ping-pong ball on the end of a pencil. He was trying, he explained, to make the sound of a ship sinking in the ocean. Robertson had to agree the result was pretty convincing.

An award-winning play for young audiences by Scotland's Catherine Wheels company, Lifeboat uses elements of make-believe to tell a real life story of survival against the odds. On Friday, September 13, 1940, an Indian cruise liner named The City Of Benares set sail from Liverpool for Canada carrying 90 evacuees. Four days into the crossing, the ship was torpedoed and sank, and all but eleven of the passengers were killed.

Bess Walder and Beth Cummings, two 15-year-old evacuees, managed to survive 19 hours in the Atlantic Ocean by clinging to an upturned lifeboat. And some 60 years later, director Gillian Robertson came across the two friends' extraordinary story in an old Sunday supplement article entitled How We Met.

Walder, who had rejected offers from Steven Spielberg for fear he would "Titanic" her story, thought turning it into a piece of young people's theatre was an excellent idea.

First staged in 2002, Lifeboat is very much built around Walder's recollections - Cummings felt less able to talk about her experiences but began to do so after seeing an early version of the show.

"What Bess does remember of the time on the lifeboat is horrific," says Suzanne Robertson, the sister of Gillian Robertson, who plays Walder to Isabelle Joss's Cummings. "They thought they were going to die, and to have to go to that place when you're a kid is unbelievable.

"They hung on to a rope they'd found, and their bodies were beaten up, but they were numb from the cold and didn't really feel much. When one would fall unconscious the other would wake her up. They watched all these adults fall away but somehow managed to keep each other going."

Grim as the story is, writer Nicola McCartney has worked hard to sustain an engaging pace for young audiences with flashbacks to the girls' family lives and the onset of war. The two actors take on some 20 roles, from the girls' parents to fellow evacuees and even the Indian stewards onboard ship. With the industriousness of child's play, props and pieces of set carry through so the kitchen table becomes part of the lifeboat.

When Walder came to see the show in Glasgow, she told Robertson, "You were very good dear but you were nothing like me". Robertson was not offended. "Of course we've taken some artistic licence, but each night in the wings, me and Izzy do feel like we're doing this for those two young girls. "Personally, I've had some really weird experiences doing this piece. Even now, when the kids say goodbye to their parents at the station, I'm in floods for real. Sometimes it's hard to get the lines out."

  • Starts 2pm and 7.30pm, tickets £8/£7. Call 01273 685861.