Mr Whyman, agony uncle for teen magazines Bliss and 19, will publish Boy Kills Man, his second novel for teenagers, on March 18. The book tells the story of Sonny, a child assassin on the streets of Colombia. Aged 11, Sonny dreams of watching his team play football and kissing girls. At 12, he has killed a man for money.
The storyline is uncompromising, and Sonny feels little regret for his actions. Mr Whyman says this is a deliberate tactic, drawn from his experience as an agony uncle. "If you tell 12-year-olds that smoking will kill them, they say that it doesn't affect them now," he said. "To earn their respect, you need to acknowledge the lure that cigarettes and drugs have.
"In the same way, you have to acknowledge that guns are glamorous. Then you can show the consequences of that glamour."
Early feedback from teenagers suggests that the novel's graphic descriptions and raw brutality have left them tossing and turning at night.
But, like his hero, Mr Whyman feels no regret:
"I could have told the story in soft terms. But that would mean nothing to a teenager. There's no excuse for not tackling reality.
"The book will keep kids up at night and disturb them. But that's good if it opens their eyes to what's going on in the world. It's healthy to provoke emotional responses."
Although set on the streets of Colombia, the novel is, in part, a response to the rise in gun crime in Britain. In the past three years Mr Whyman has seen a marked increase in the number of gun-related agony queries he receives: queries, he says, that stand out among those about first kisses and wet dreams.
"The story is about the impact of guns on one person's life, but it's also about a universal experience," he said. "It could be set in New York or Tower Hamlets. It provides a springboard for debate."
Matt Whyman will be speaking on teenage fiction during a World Book Day conference at the Institute of Ideas, in London, on March 4. Geraldine Brennan, TES books editor, is also speaking.