Stephen Leather writes: I've always been intrigued by the fact that major criminals often turn out to be family men, too. They break the law, they do bad things, but they're also somebody's son and more often than not they're somebody's father, too.

In Den Donovan I wanted to create a villain who has a very human side, struggling to bring up his young son while at the same time trying to hold together a criminal empire that's coming apart at the seams. I also wanted Donovan to undergo some sort of redemption, if not to see the error of his criminal ways then at least to realise that some things are more important than money.

I've also always been fascinated by the sort of people, men and women, who are prepared to work undercover. Villains, until they get caught, tend to have much better lives than their law-abiding counterparts. They live in better houses, drive better cars, eat at better restaurants and, truth be told, get to sleep with prettier people. It takes a particular sort of person to work undercover and not be tempted to switch sides.

Tango One is a coming together of the two themes. Three undercover cops are sent against Donovan, and each, in their own way, becomes seduced by his charisma, leading them to question what they are doing.

It turned out to be a difficult story to write, mainly because I wasn't sure how it should end. I guess I too became seduced by Donovan and didn't want him to end up behind bars!

After about six months writing the novel, I turned to my good friend and fellow Dublin-based writer Glenn Meade for suggestions on where to take the plot, and as always he was a great help. Sometimes writers can get too close to their work and they need a dispassionate outsider's view to keep them on the right track. Anyway, I'm proud of the way that Tango One turned out, and I think it's one of my best thrillers.