As dawn broke on October 10, 1996, the sisters at St Mary’s College made a horrifying discovery. The dormitory wall had been broken down, the barred window removed and used as a ladder down which 152 girls had been dragged into captivity by rebels from the Lord’s Resistance Army.

Sister Rachele, a slight and mild woman, set off in pursuit. Thirteen girls managed to escape. Later that day, she caught up with the rebel’s commander, and the 139 girls he was holding. She implored him to release the children. Ultimately he agreed to let her have back 109, but insisted on keeping 30, carefully choosing the strongest and the most beautiful.

Grace, a tall 16-year-old, was one of the girls he kept. She told me her story. As Sister Rachele left with the released girls she heard Grace crying out to her and looked back.

The teenager was on the ground and a booted soldier was jumping on her sobbing body. This was but the beginning of a story of appalling cruelty.

First, the 30 Aboke girls were instructed to kill a girl who had attempted to escape. When they demurred they were beaten until they gave in and themselves beat the poor girl to death.

Then began the long and gruelling trek to rebel camp Number 8 at Aru in southern Sudan. Some children died of exhaustion on the trek, others were swept away crossing the fast-flowing waters of the Nile.

At the camp, the girls were handed over to rebel commanders as “wives”. The normal practice was that rebel leader Joseph Kony had first choice. He already had more than 50 wives but he still took four of the Aboke girls. The senior commanders had the next choice, their juniors taking the girls who were left.

All the girls were raped and began an existence of sexual slavery: nearly all who would be fortunate enough to return would be found to have syphilis.

Grace was chosen to become a soldier and given an AK-47. Training was rudimentary. “They told us ‘Anger will show you how to fight’,” says Grace who will never forget the gun’s serial number: 760005.

She was not given a uniform and there was little food or water at the camp. On one forced march she became so exhausted she sat sat down and fell asleep leaning against her assault rifle. Other fighters thought she was dead and she was buried alive in a shallow grave from which she emerged choking and terrified.

In April last year she was caught up in the advance of the Sudanese People’s Liberation Army - enemies of the Khartoum government and, therefore, of the LRA. The camp came under fire.

“Everything was burning. Kony was packing people into a pick-up, but I hung back. Suddenly an SPLA armoured car fired into the pick-up killing everybody.”

Grace ran from the camp with her gun, some bullets and a saucepan on her back. Suddenly there was an explosion as a shell dropped next to her and she was thrown to the ground. “I thought I was dead and then I saw that the saucepan on my back was dented. It had stopped the shrapnel.”

She travelled for three days in the bush. At one stage she came to the Nile and almost despaired. “But by a miracle I found a shallow place and was able to cross.”

Another day, she came across a Sudanese village where the local dinka men seized her. A firing squad was lined up and she was put in front of it. As the weapons were cocked an old man appeared and she appealed to him: “I am a girl from Aboke School in Uganda. please help me...”

She was taken to an SPLA barracks and then to meet John Garang, the SPLA commander. “He said I would be saved because I was a Christian.”

As she recounts this amazing story of survival, it is clear that her faith was as important in her survival as her physical strength. And her last sad words to me were: “What I saw with my own eyes cannot allow me to forget the girls still in captivity.”