Picture yourself riding horseback through a canyon in the heart of the southwest. The air is dry and hot, and you hold the reigns lightly, your horse letting out a contented whinny. With each step, his hooves stir up small clouds of dust.

To your right, an emerald stream winds its way along the canyon. It is the only water for miles around, and to both sides, the canyon walls rise steeply, vivid layers of reds and yellows, so high that you can hardly see where they end. And above you, barely visible, is a strip of bluest blue sky.

You are on your way to discover the lost city of Quivira -- Coronado's much sought city of gold...

Douglas Preston and Lincoln Child have another hit on their hands with "Thunderhead". Peppered with bits of Native American legend and archeological facts, "Thunderhead" is the story of Nora Kelly, a young archeologist whose career is hardly what she'd hoped for. An assistant professor at a prestigious archeological institute, she is making a go of it, but barely. She doesn't even have enough money to take care of the family's potentially condemnable ranch, bequeathed to her and her brother by her parents.

The ranch is a source of all sorts of problems for Nora. When she is summoned there in the middle of the night because of strange noises, Nora is in for the surprise of her life, as an unexpected piece of her past sends her on the journey of a lifetime.

Soon thereafter, she is leading an expedition deep into the heart of the southwest, in search of the legendary city of Quivira. And along the way, are those who do not want Nora to succeed.

I discovered the team of Douglas Preston and Lincoln Child when "Relic" was first released. I'd never heard of either author, but the premise sounded interesting, lying somewhere between science and the supernatural. Now I'd be lying if I said that "Relic" was beautifully written and perfect in all regards. It wasn't, by far, but the two things I could give the book credit for were pacing, and imagination.

And that holds true for the books that followed as well. Preston and Child pace their books wonderfully. From the opening pages all the way through to the end, "Thunderhead" is a whirlwind -- or, as they say in the business -- a real page-turner. The chapters are kept short, which I particularly like, and they don't waste words, which is of utmost importance in an action/adventure novel such as "Thunderhead".

There is a great deal of descriptive writing in "Thunderhead" -- enough that you can really picture what is happening. You can see where the expedition is going, what they're doing, the triumphs and perils that befall them. The imagery is wonderfully vivid -- but they don't ever lose the story in the images. The perfect balance of imagery and plot is difficult to achieve, but here, the balance is perfect.

It's not a perfect book, though. Although their writing has come a long way since the pages of "Relic" and "Mount Dragon," their characterization still leaves something to be desired. I found many of the characters to be stereotypical -- the stubborn, by-the-book scientist, the struggling-but-determined young woman, the tobacco-spitting cowboy horse-wrangler... Preston and Child seemed to have struggled so hard to make each of these characters individual, that they don't seem real for the most part, though I must say that it was nice to see them reprise the character of Bill Smithback, who you might remember from Relic. Still, lost is the subtlety that would make most of these characters come to life.

Subtlety is one thing that this book could have used more of. Subtlety in characterization and subtlety in foreshadowing. I love foreshadowing as a technique in novels. I love to get to the part of a book where I thump myself on the head and say, "I should have seen that coming." The problem with "Thunderhead" at times is that their foreshadowing is too obvious, and you see it immediately. (I'm not going to give you an example, for fear of ruining the book for you).

My other gripe is that -- although for the most part, the plot is fully realized -- they built up the part of Nora's brother, and in the end, never fleshed it out. I like books that come together completely in the end, and this particular thread was tied up a little too haphazardly for my liking.

On the whole, though, it is easy to forget all the shortcomings, since "Thunderhead" is such a wonderful read. They leave few dusty corners unexplored in this marvelous adventure, and you'll be sure to find yourself swept right along, like a toy sailboat in a flash flood.

Douglas Preston and Lincoln Child are a duo to be watched. With each book, they're getting better and better, and I, for one, will be sure to pick up my copy of their next release...because like an expedition in search of a lost city, you never know what's coming next.