When Ishmael Beah got caught up in Sierra Leone's civil war he was a 12-year-old boy obsessed by rap music. Within a year, he was a drugged-up killing machine.
Beah spent more than two years as a child soldier, psyched up on Rambo films and high on anything he could get his hands on. He doesn't know how many people he shot dead.
A Long Way Gone: Memoirs of a Boy Soldier is his account of the 1991-2002 war when he fought with the army against the Revolutionary United Front (RUF), a rebel force notorious for hacking off civilians' hands and limbs.
Listening to Beah tell his story, it's impossible to reconcile the slightly built and gentle young man in front of me with the mass killer he says he was. He is eloquent, open, humble and funny. And he has a truly stunning smile.
But then this disconnect is part of the reason he wrote his book in the first place.
"A lot of people's perception of Sierra Leone is civil war and amputation and there's no context. It seems as though it's just a place where everyone is mad and that's not the case," he says.
The first time Beah killed someone was in a battle in a swampy forest after seeing his friends, boys aged 11 and 13, blasted dead by rebels.
Back at camp he was given drugs which suppressed the horror of what he had seen and done. The drugs fuelled the child fighters throughout the war. They smoked marijuana, popped pills and snorted "brown brown", cocaine mixed with gunpowder.
"All these things were just to numb you. It worked very well. If all your faculties had been in place you could not have lived with this madness," Beah said at a talk in London this week organised by the Institute of Contemporary Arts.
The drugs gave the children boundless energy, a feeling of invincibility and even made the war seem like a game at times.
Beah describes taking part in a competition to see who could execute a prisoner fastest and recalls the sense of pride he felt when he won.
"I think that's one of the things I wanted to show in the book - all of us are capable of losing our humanity," says Beah, now 26 and living in New York.
"Before the war none of us thought we were capable of doing such things."
Beah's descent into hell began in 1993 when his home town was torched by rebels - he never saw his family again. Oddly, his own life was saved by his love of rap. He was away at a talent contest with his dance group when the rebels struck.
Along with other boys, the orphaned Beah spent months running from the violence, his only possessions some rap cassettes. At one stage they were caught by villagers, who were suspicious they were rebels. When the tapes fell out of Beah's pockets the village chief demanded to know what they were.
"In the middle of this war, there I was miming 'I need love' by LL Cool J," Beah recalls. "I've always though how ironic it was that I was miming this song because I really did need love at that time."
The boys finally arrived at an army camp, hoping to find safety. Instead they were given guns and sent into battle. Killing soon became "as easy as drinking water".
Beah's war came to an end in 1996 when he and other children at his unit were rescued and moved to a rehabilitation camp. You might think they would have been relieved, but far from it. They were absolutely furious - they didn't want to lose their surrogate army family or their status as combatants.
Remarkably, the ex-army boys were put in with rescued RUF child soldiers and all hell broke lose. But Beah later realised they had all been brainwashed in the same way. Both the RUF and the army had told their child fighters that killing the other side was a way of avenging the murder of their own families.
In the camp the boys ran wild. They beat staff up, stabbed them, trashed and burned property and fought each other day and night.
The violence helped them avoid confronting their demons. And of course, the children were also withdrawing from drug addiction.
Some staff were attacked so badly they ended up in hospital, but to Beah's amazement they never gave up.
"They would come back from hospital and say 'Oh, it's not your fault, you need time to recover.' They saw something in us we failed to see. That persistence rekindled our humanity," he says.
One striking aspect of Beah's account is his ability to find humour amid the darkness. He told how the camp organised football matches for the boys against outside teams. The trouble was that every time the boys lost a game they fought all evening.
The exhausted staff eventually resorted to telling the opposing teams to lose on purpose - something Beah only discovered much later. "I had come to believe we were quite good footballers," he remarks with a wistful smile.
Today, he considers the staff his heroes. "They were willing to look at us as children regardless of how we had behaved," he says. "If these people had given up after two months I wouldn't be standing here."
Instead, he might be hanging around on a street corner in Freetown, poor and jobless like the young men he saw last year when he returned to his homeland for the first time since leaving a decade ago.
Beah is now launching the Ishmael Beah Foundation to provide education and vocational opportunities for those who have lost their childhood to war.
So what does he think of the army lieutenant who robbed him of his own childhood and sent him into combat? Beah is philosophical.
"I do blame him up to a certain point, but I don't think I hate him and I am not bitter," he says.
"When you are bitter you want revenge and that does not solve the problem - it just exacerbates the madness."