I wrote this book because almost a decade ago I saw a beheading video. The man who died was a British truck driver in Iraq, and all I could think was here someone had once raised this man from the time he was a boy, loved him, had all these hopes for him, and this was how his life turned out. Made into a propaganda piece by people who were going to get away with it.

It stayed in the back of my mind, I guess, for years.

Sometime after that, my dad came across an article in The Economist about a stem cell experiment where they injected human stem cells into the brains of aging mice and slowed cognitive decline. Since my grandfather had a pretty devastating case of Alzheimer’s, we read about this new stem cell technology with a lot of interest. And since we’re a pair of freaks, we had all these running jokes about it. Like, perhaps I could stand outside fertility clinics with a turkey baster and ask women going in if they could spare a few embryos, so my family could inject them into my old man’s brain. (I’d then point to him sitting feebly in a nearby car.)

Eventually I got it in my head to join the stem cells with the idea of someone avenging a family member’s death abroad. I made the title character, Tom Reese, an orphan whose brother has been involved in a stem cell experiment and has since been murdered in Paris.

My thought was: what if this little person, this nothing in the grand scheme of things, rose above his low station in life and came from a world away to find the people responsible?

I liked it. But as I wrote, I realized there was more to this story. All that was wish fulfillment—very plausible wish fulfillment, I hoped—but what’s the reality? This young man is running around Europe, stealing state secrets and hunting people down on scant, sometimes circumstantial, evidence. Bad things are going to happen. Actual bad things, not just some bureaucrat none of us care about getting offed on page 210.

Look at anything—wars, medical progress, technological change—and you see that no matter how worthwhile the cause is, innocent people get hurt. And what occurs in the book is Tom gets an innocent person killed.

When I put that in, I was thinking of a quote by King Ferdinand: “Let justice be done, though the world perish.” Ultimately Tom has to decide how far to push his agenda, not based on its merit but based on its cost, both to himself and others. That ultimately is what it takes for him to become a man in his own right.