Caroline Todd and her son, Charles Todd, write under the name "Charles Todd."

Who was created first, your tormented WWI veteran, Inspector Rutledge, or Hamish, the dead "sidekick" he hallucinates about in your mystery series set right after that war?

Basically, they came together at the same time. What we wanted to do was to write a mystery, and then we started talking about what historical period we wanted to have as a setting. We came up with the possibility of 1919, which is modern, but at the same time, it's before forensics really became a strong part of detecting, so that our detective could be a man who has to think through things.

You can't come up with a mystery and then pick a time frame—you have to pick what works in a particular time frame. Hamish really came in as a way to describe what Rutledge was going through, to describe his mental processes as he was trying to solve crimes. Hamish, who was executed by Rutledge [for insubordination during WWI], is essential. A main theme of the books is anguish and redemption. We get a lot of e-mail from Vietnam war veterans, surprisingly, and a lot of e-mails from Germany, where the books do very well. More than anything else, it's human triumph in the face of adversity that appeals to some of our readers.

Everyone has traumatic experiences. Trauma is war, but it's also losing a child, going through 9/11, any kind of loss.

How do you divide the writing?

We don't actually divide it. If we can get the first page down, the rest of the story falls into line, the first page sets the tone and we start thinking what would come out of this situation or conversation. We'll write something and discuss something and see if it sounds the way it would if it happened in real life. Whoever comes up with the best solution, that goes into the manuscript.

One of the greatest compliments we get is when people tell us they can't tell where Charles stops and Caroline starts.

You introduce a possible romantic interest for Rutledge in A Cold Treachery. Can he ever find happiness?

We've been asked that a lot. If you really understand the psychological damage he's suffered, it's clear that he's not really looking for a relationship to heal him.

Could you explain why each book in the series takes place in the month immediately following the previous entry?

Basically because of the situation that we had set up. If we had done what most authors do and pick him up in a year's time, then the reader would have no way of assessing how he had changed, how he had grown. Once we've finished with 1919, we can give him more time. Rutledge has changed a lot during this period. As a medical specialist once told us, the strong were able to fight through shellshock and post-traumatic stress syndrome. They didn't heal, but they found a way to live with it and this is what Rutledge has been trying to do. He's been trying to come to terms with what would have driven a great many people mad or to suicide.

One of the things we picked up from veterans who have written us is that it takes a while to recover—there's no magic pill.