WHEN Simon Clark was invited by prison bosses of a maximum security jail to give a talk to inmates about writing, he was happy to help out.

This was back in 2001, just after the publication of The Night of the Triffids, Clark's highly acclaimed sequel to John Wyndham's famous novel The Day of the Triffids. But when he turned up, it wasn't quite what he expected.

"I thought it would be guys who had nicked a car or stolen a chicken from a supermarket or something like that. But it was lifers, serial killers and psychopaths."

He admits that coming face to face with violent psychopaths and multiple murderers was unnerving.

"I wasn't sure I could do it and part of me wanted to jump on the train and go home. But another part of me wanted to know what they would be like.

"When I first went in, I felt quite intimidated because of who these people were and what they might have done. But there were a couple of prison guards there and I thought, 'Oh well, at least they're in
front of me,' but they all sat behind me."

However, Clark was surprised when he came face to face with these killers.

"My perception was probably similar to other people's, I thought these
men would be brutal thugs covered with tattoos. But the shocking truth is they came across as pleasant, amiable, well-read gentlemen. That was probably the hardest thing to deal with and it took me a long time to get my head round this."

Clark made a dozen visits to the jail and spoke to 15 murderers and serial killers over a period of months, but it has taken him seven years before he's felt comfortable drawing on these experiences for his latest novel, Lucifer's Ark.

"One of the hardest things to deal with was the fact that these serial killers weren't what I expected. They aren't the guys who pull the wings off butterflies, they're the kind of people who go out and feed the birds. They develop this cloak of invisibility which
is very disarming," he says.

"The prison guards told me these people wouldn't jump on you in an alley, they consider it almost impolite to kill a stranger. Instead, they want to form a bond and get some kind of rapport, which is
why I was warned not to give any personal information about me and my family."

As he spent more time in their company, he began noticing certain things. "Some of them had been inside for 20 years and they hadn't seen sunlight, so their skin had this grey, metallic pallor."

There were also other more disturbing traits.

"I'm basically optimistic about the human race and believe if you put different people together that good will prosper. But you could see with one or two of these guys that they weren't looking out they were
looking in, and from the expressions on their faces you felt they were looking at something dark and horrible."

After meeting some of the country's most dangerous criminals, he decided to do some research of his own.

"It's been said that some of the most successful businessmen and politicians in the world have psychopathic tendencies.
Idi Amin used to eat the livers of his victims because he thought it gave him power," he says.

"Many serial killers suffer from low self-esteem and if they shave their victims' heads and keep the hair in their pocket – in their
own minds, at least, this makes them charismatic and intelligent.

"Sometimes they want to share this with the world because they think they've discovered some new and amazing power that can cure the world's ills and they don't know why no-one else understands.

"For instance, there's a guy in California who killed 13 people and he believed that every time he killed someone he stopped an earthquake happening and he thought he was a hero, rather than
a psychopath."

Clark says serial killers are different from other murderers. "If somebody kills a person after getting into a fight on a drunken night out, they are usually full of remorse but serial killers have no sense of guilt over what they've done."

His research also revealed some interesting connections. "I found that it's often in times of great personal stress, or when society is going through turbulent changes, that you get clusters of serial killers. If you look at isolated communities like the Aztecs, the whole society ended up becoming psychopathic and resorted to cannibalism and human sacrifice.

"It's as if we have this latent ability to become psychopathic in extreme situations, like during a war. A lot of people can take that step into psychopathic behaviour but once the stress has gone they revert to being normal. In ancient Egypt, when there was a famine, the people believed that if they ate x number of their children they would survive, which sounds unthinkable to us today."

Psychopathic tendencies, he says, can manifest themselves in different ways.

"You can have someone who ticks all the psychopathic boxes, but they might just throw tomatoes at road signs and that's the worst thing they will ever
do. But you can get someone else and they will skin someone alive."

Although Clark, who lives with his family in Doncaster, made his name as a horror and thriller writer, he admits he wasn't sure how to use his experiences in his work.

"It's a writer's thing, you see something horrible and you're shocked, but then you go away and think how you might be able to use it. But shaking the hand of a real-life killer is unsettling and it took a while to reconcile the fact that these seemingly pleasant guys had done such terrible things. So when I came to write the book, there was a sense of relief."

Lucifer's Ark involves a cargo of serial killers who are being secretly shipped abroad on a passenger ship and become embroiled in a life or death struggle when the boat is hijacked.

For Clark, storytelling has always been something of a second nature.

"I grew up in Wakefield and I came from a family of story-tellers. My uncles would come round and tell stories about a haunted house or a murder and one of the things I picked up on from an early age was if you told a good story, it was a way of getting people's attention."

However, he admits that meeting serial killers in the flesh has affected the way he sees people.

"It does make you wonder. I come from Yorkshire and it's a trait in this part of the world to treat people as you find them and if someone's pleasant, you think they're a decent person.

"But now if someone's overly courteous there's something in the back of my mind thinking, 'Is he genuine, or is there something amiss?' I wouldn't say it's made me more suspicious, but your view of the world does change ever so slightly."

Lucifer's Ark by Simon Clark is published by Severn House priced £9.99.