First chapters revealed from romantic time-travel thriller 'Tempest' -- EXCLUSIVE

The most important element of any time-travel story is the rules: what can the hero do, what's impossible, and how does messing with the past change the future?

What we find in this exclusive excerpt from the opening of Tempest, the debut YA novel from Julie Cross, is that its cocky, time-shifting 19-year-old protagonist doesn't understand the rules himself, and is struggling to figure out this strange, apparently instinctive power — though, like most kids that age, he's not all that serious about his potential until trouble strikes.

Expectations are high for the novel, which has already had its film rights optioned by Summit Entertainment, the studio that produces the Twilight films. By releasing such a significant portion of the book four months early — and for free — publisher Thomas Dunne Books is, sort of like the hero of Tempest, hoping some actions taken in the past will positively influence the future.

See below for more theories on the excerpt.

As found in the opening page released last June, we are introduced to Jackson Meyer, the charming, somewhat reckless, young man who is as baffled by his ability to become unstuck in time as anyone, though it's largely a secret between him and a physics expert friend named Adam. As the story begins, we see Jackson and girlfriend Holly working as camp counselors during a youth-group visit to the zoo, though Jackson is preoccupied by efforts to test his power.

The theory: though he can shift backward in time (usually by only 30 minutes or so) nothing he changes in the past actually shows up when he returns to the present.

That raises all sorts of questions about the story. For one, is he really time traveling? Adam describes him going into a vegetative state during his backward jaunts, so could the past Jackson sees really be hallucinations or dreams? Or is he splitting off alternate timelines when he shifts back, nature's way of avoiding the paradoxes that would inevitably arise due to changing the past?

It's all just a big science experiment punctuated by a flirtatious romance between Jackson and Holly — until the final pages of the excerpt.

A pair of mysterious men burst in on the young lovers as they lie in bed. A fight ensues, a gun is drawn, and blood is spilled.

Jackson escapes by reeling backward in time, but imagine the heartbreak of seeing that person you love again, and knowing you can't save her.

On Twitter: @Breznican.