Since 1990, Randy Wayne White has produced 17 thrillers featuring Florida marine biologist Doc Ford, most recently Deep Shadow.

How do you keep the characters fresh?

For me, intellectually and emotionally, Ford and Ford's sidekick, Tomlinson, are living entities, so there's never a need to effect a sense of “freshness,” because they evolve naturally, on their own, each man following his path, sometimes slowed or goaded along by his personal flaws or strengths.

You spent 13 years working as a fishing guide. How did you make the leap to writing fiction?

I was a full-time guide, did almost 3,000 charters, and was on the water 300 days a year. Since childhood, however, I always wanted to write books, perhaps believing that, if I wrote, I might become a part of the magic I found in books. I worked very hard at writing in my spare time and, in 1978, got a break when Rolling Stone founded Outside Magazine and published a piece by me. While guiding, I began to publish regularly in some of the country's premier magazines. In 1987, Tarpon Bay Marina was closed to powerboat traffic, and I was out of a job. As much as I miss the marina, losing my job was the best thing that ever happened to me. I had to make my living as a writer. I had two young sons, and failure wasn't an option.

Deep Shadow is an unrelenting, terrifying read. Are you ever going to ease up on Doc?

I have story lines in mind for a dozen or more Ford/Tomlinson novels. The next Ford book will probably have to do with the horrific trials endured by illegals from Central America, men and women who risk everything, including their lives, to have the opportunities and freedoms we enjoy daily. I choose subject matter that I find emotionally and intellectually compelling (occasionally to the disappointment and even outrage of my readers), and I'm forever elevated by the heroics demonstrated daily by good men and women, devoted to their families, who never make the headlines. As for easing-up? Doc and Tomlinson lead fairly quiet, normal lives, with good long stretches of work, fun, and sunset parties—but only between books.

What advice would you give to writers trying to break into the business?

I have a close friend, Don Carman, who was a brilliant pitcher for the Philadelphia Phillies; he signs baseballs: “Be relentless.” I can think of no better advice to an aspiring writer: be relentless.