Every once in a while you read a novel or see a movie that keeps you glued to the story with such excitement that you can't turn away until you know how it turns out. Everything is moving so fast, and you're so swept up in rapidly unfolding events that you don't dare leave the story for even a moment. The tension builds; you feel every jolt until a breathtaking climax leaves you exhausted.

That, my friend, is a thriller.

How did that movie grab you by the neck and take control? Why that novel and not a hundred other novels?

There isn't a simple answer. There never is when you're examining a work of art. I don't pretend to know all the secrets of a great thriller, but I've learned a few things I'll share with you.

The first and most important ingredient is emotion. If you don't feel the story in your gut, it's not a thriller. And not just any type of emotion. A great romance can break your heart, but that's not the emotion that fuels a thriller. Not that romance can't be part of a thriller, but it's not the what's-going-to- happen-next excitement of a thriller.

A great thriller builds up to an emotional high that lifts you up and takes you along for the ride. Consider Rick Deckard "retiring" androids in Blade Runner or Clarice Starling hunting Buffalo Bill in Silence of the Lambs. At first we tag along with Rick or Clarice, then gradually bond with them and feel every emotion they experience. They are both vulnerable, flawed characters, but we can feel for them, and ultimately, feel with them. Their highs and lows become ours.

A great thriller is unpredictable going forward and completely logical looking backward. Who would have guessed that a creature would burst out of a guy's chest in Alien? Or that the FBI agent in charge of the investigation would be the killer in The Poet? On the other hand, as you look back, it's believable that this alien creature could be so dangerous or that the FBI agent was the killer.

The plot also features deadlines. If they don't capture the villain soon, something terrible --- an assassination, a virus outbreak, a nuclear explosion - is going to take place. You can almost hear the clock ticking. Or is that your pulse?

A great villain is a necessary part of a first-rate thriller. Perhaps a charming psychopath such as Dr. Hannibal Lecter from Silence of the Lambs or megalomaniac Dianne Morgan from Unholy Domain. The villain must be more than a match for the protagonist, who battles overwhelming odds while in constant danger. A great villain will stir feelings of hatred, fear, revulsion and maybe a little admiration in the reader or moviegoer.

The setting and all the action must be believable. For example, if the action takes place in a specific locale, then all the details (streets, landmarks, major buildings) had better be correct. If bad writing forces the reader to stop believing, then all the air comes out of the story.

And, of course, there is the climax. It must be exciting, unpredictable, resolve the major issues and yet remain consistent with the storyline. Fatal Attraction and Jaws have terrific climaxes that bring the story to a thrilling conclusion.

So that's it --- a few insights as to what makes a great thriller. Difficult to describe, but when you see one, you know it.

Dan Ronco is a writer of technology thrillers and near future science fiction. PeaceMaker, his first novel, was published in 2004 and his second, Unholy Domain, will be released March, 2008. Dan mixes visionary ideas with a touch of romance and humor. Learn more about Dan at http://www.danronco.com