When I meet Dave Rudden, he has just minutes beforehand been handed a copy of his debut novel, Knights of the Borrowed Dark, for the first time. It's the day before an industry launch in London and a week before the book is officially released and he seems a bit dazed by the whole experience.

Two years ago he signed a six-figure book deal with Puffin for his fantasy novel series. He was in the €2 shop on Georges Street, Dublin, with his then girlfriend when he took the call from his agent about the deal.

“We had a euro between us and, no word of a lie, we were trying to decide between the €1 slightly fancy soup or the absolutely dust-flavoured 50c soup and a demi baguette and I got a phone call. It was my agent who was saying we had a deal from Puffin and I was like, ‘Right, what do you think we should do?’ She said, ‘Well I think we should take it Dave.’ It was literally life changing,” he says.

Rudden studied teaching in St Patrick's College in Drumcondra and taught for a year his local school in Cavan before packing up to go to Egypt for a year. When he returned he got involved in Dublin's literary scene and began indulging his penchant for writing fan fiction. The idea for his first novel only came about after his computer crashed and he lost 80,000 words of Warhammer fan fiction.

“I realised if I actually wanted to make this a career, I needed to go big or go home. I applied for the creative writing masters in UCD, reasoning that if they turned me down, that was a fairly good indicator that I should go back to teaching. Then I got in, and they asked me, as an assignment, to write the first chapter of a book and everything happened from there.”

Writing at a young age became a way of working through his emotions. He was badly bullied at school – “I was ginger, I was overweight, I was extremely shy, I was the only person within 100 miles who was into fantasy and science fiction” – and he began to think that this was just how his life was going to be.

“I remember very clearly at 12 thinking there were people who were meant to be happy and people who weren’t and I was just in column number two. I was an extremely sensitive kid and I like to joke that I was so emotional that I need to invent people to put [the emotions] in.”

Although he was more readily accepted at college, Rudden says he still felt very negatively about himself and suppressing those thoughts led to a deeper depression.

“On the outside I was functioning, I was going to college and I was socialising but because my self worth was so low, if someone looked at me the wrong way, that was me gone for a week, just pacing in my room, going ‘this is it, everything is going to end now’.”

He began self-harming. “Cutting helped with that, it was pain that I could control basically. It got to a point where I realised I had to do something otherwise, if I didn’t, I would just die. I discovered writing and I told my parents.”

His experiences are written indirectly into the book. He and the main character Denizen are similar, sharing an anxious disposition; a penchant for overthinking, and a sneaking suspicion the world doesn’t quite make sense.

In the book, Denizen is one of the Knights of the Borrowed Dark, a group fighting for good with magic powers. Those powers, however, begin to turn you to iron, something he called the “cost”, which is a nod to self-harm.

“The cost is never portrayed as a negative thing, but more something to be aware of. You are changed by going through trauma and they do wear it. They may get injured but they keep going. People have said to me before, ‘Would you ever get skin grafts to cover your scars?’ and I always say no because I’ve been through something and they’re a reminder. I’m not proud of them but nor am I ashamed of them, they just are. The past just is and you can allow the past power over you or you can accept it’s a thing and move forward. They’re just a fact, they’re just a part of me.”

It’s something he’s keen to start a conversation around, because growing up in Cavan he feels, particularly for young men, there isn’t a space to discuss mental illness.

“Young men are encouraged to just suck it up and repress it and go play sports, or just survive, and it never works. Suicide statistics for young men in the midlands are horrific, and for college students. I didn’t give my parents a chance to respond until I absolutely had to and I think teenagers need to know they have a space to talk. Weakness and vulnerability are different things and there’s no weakness to admitting you’re in pain,” he says.

Knights of the Borrowed Dark is written for children aged 10 and up and does explore quite dark themes.

Rudden has found benefit in being trained as a teacher in writing his trilogy. He believes that having respect for children is most important and has written the books with a level of complexity that reflects that, something he says his favourite authors as a kid, Eoin Colfer and Lemony Snicket, always did.

“I know there is an unwillingness to expose kids to the darkness of the world too early but I think people forget being a kid is an incredibly scary thing anyway. When you’re five, you literally think things are going to eat you at any point.

“The darkness in fiction doesn’t tell kids there’s darkness because they already know there is. It just tells them that sometimes there’s darkness that has rules or darkness that can be beaten if you’re clever and brave and you stick with your friends.

“The main thing is respect: treating a child not as if it’s a weird other species but as if it’s an actual person that has dreams and hopes and goals that may be different than what you’re dealing with day to day, but that are still really important and relevant.

“ It’s a thing kids have to put up with so there’s no point keeping it out of books because then they won’t be prepared for it in real life,” he says.

Knights of the Borrowed Dark is published by Puffin/Penguin Ireland