"My major motivation is to be closer to family," he explains. "My brother is there, my mother is there. We're hoping to break ground in March, and it will be completed right around the time we're finishing the last season of Lost, in March 2010. I really miss that kind of wide-open space, and there's a big part of me that wants the kids to live in that mountain air. But we'll be able to get to Portland, and Seattle. . . . It's not as culturally remote as where I grew up."

That would be the rural ranch in Crowheart, Wyoming, where, as a high-school kid slouching toward oblivion, feeling out of place as a football jock and out of touch with ambition of any kind, Fox joined his brothers in demolitions to relieve the boredom. "We were pyromaniacs," he says, breaking into a very wide smile. "My dad kept a lot of dynamite on the place. We'd vent empty 50-gallon drums with axes, turn them upside down, and blow them up."

Sensing that he had no idea what to do with his life, Fox says, his Ivy League-educated father sent him east for a year at an elite prep school—at which point his life began to take as many twists as a Lost story line: Chewing tobacco and playing football at Deerfield Academy led to Columbia, and an economics degree that promised a job in the financial world . . . until a modeling gig veered him toward acting classes, which earned him a role on Party of Five, opening the door to an ensemble part that became a star turn on a pioneering sci-fi series that, well, seemed to be leading nowhere.

Thankfully (for Fox, for the cult followers, for casual fans), the fourth season jumped off the page with the more urgent narrative that followed the announcement that the 2010 season would be Lost's last, a development welcomed by its star. "Personally, it's a relief," he says. "I owe this show a great amount, and I think it's exceptionally good . . . [but] I am looking forward to the freedom that comes with not working on one project professionally.

"All of us knew that if the show was strung out indefinitely, it was going to ruin the story. It's not like a doctor drama, where you have a new case each week. This show started with a plane crash on an island in the South Pacific, and it's going to have a very global and epic ending."

An ending he knows? "I have some idea," he says, laughing.

None of this is to suggest that Fox has grown weary of the multilayered fable that has vaulted him into the pop-culture pantheon. Dramatically, at least, he feels as if he's just getting started; the quantum leap in the show's story line offered him myriad chances to polish his game. "When it's all said and done, you'll be able to look at the six seasons of Lost and see a pretty amazing character arc," Fox says. "Jack has been evolving, and not necessarily into a good place. We started the show with him being this hero who had no concept of what that required, sort of trying to live up to the expectations . . . and then finding the way to redeem himself."