We're watching a movie trailer: A party full of young, sexy Manhattanites is suddenly disrupted by a massive explosion. The revelers run into the street as someone yells: "I saw it, it's alive, it's huge" -- and the disembodied head of the Statue of Liberty comes flying down the street.

The trailer reveals it's for a 2008 Paramount film from wunderkind producer J.J. Abrams ("Felicity," "Alias," "Lost"), and virtually no other details, so we're left wondering: What's the name of the movie? Who's the villain? What freedom-hating beast(s) -- HulkGodzillaKong? the Cthulhu? Taliban evildoers? -- would decapitate Lady Liberty?

But some fans want to know more than what's up with the movie. Go online and you'll find people for whom the biggest question is not whodunit, but: Hey, is this trailer the first clue in the latest alternate-reality game?

For those unfamiliar with the genre, alternate-reality games are perhaps best illustrated with an example: Imagine you find a Web site whose owner says it's been hacked and asks the online world for help. People search the site and find corrupted data files, and a countdown to the year 2552. The site is like many small sites that run into tech problems and need help.

Except the site is fake. The owner is fake. Her entire world is a fictional creation, a web of fake sites and fake blogs, with more and more mysteries slowly unraveling, as online participants decrypt codes in the corrupted data files. As it happens, 2552 is the year that an alien horde invades Earth in the Xbox video game series Halo. Indeed, the entire fictional world was part of an alternate-reality game called I Love Bees -- promoting the 2004 launch of Halo 2 and deepening the mythology of the Halo world -- created by a firm, 42 Entertainment, devoted exclusively to the creation of "immersive entertainment."

Many fans found I Love Bees when an advertisement shown in movie theaters for Halo 2 briefly flashed the URL of the Web site that was experiencing the problems -- and would spend the next four months unraveling the mysteries within.

(The initial mystery that kicks off an alternate-reality game is known as the "rabbithole" or "trailhead." Die-hard fans are always on the prowl for new games, but those new to the genre may stumble into a game by Googling something that catches their attention -- a cryptic movie trailer, for example.)

Jonathan Waite, owner and senior editor of ARGNet, a news site devoted to alternate-reality games that is one hub of the community, got involved with ARGs in 2001, when an elaborate game known as the Beast was being produced to promote Steven Spielberg's "AI." The movie's posters featured clues that led to a chain of Web sites where players investigated an elaborate murder mystery.

"It was the creation of a new genre of gaming: a game that took place in real time, across different media, using different interaction methods, with real world events -- there were actual rallies in certain U.S. cities that took place that coincided with the game," recalls Waite, 30, a schoolteacher from La Broquerie, Manitoba. "It really captured the imagination of a lot of gamers."

The genre has since grown dramatically. The "puppet masters" of the game for "AI" formed the Pasadena, Calif.-based 42 Entertainment, which has a staff of 25 and has produced a half-dozen other games in addition to I Love Bees. Susan Bond, the firm's chief production officer, says that Bees drew an audience of around 2 million who were involved at some level with the online experience, according to the company's internal data. Research from 42 Entertainment suggests that the players range in age from 17 to 55, with an almost even split of male and female players. "Great storytelling has a universal appeal," Bond says.

But 42 Entertainment is not behind the mysterious Abrams trailers and sites: "Not something we're involved with," Bond says. "It is interesting though, isn't it?"

Abrams has been known to dabble in this world before. His TV show "Lost" last summer ran an alternate-reality game of its own called the Lost Experience, from Hi-Res, a London-based marketing firm. The game revolved around a hacker who enlisted the help of the online community to investigate "Lost's" mysterious Hanso Foundation.

Hi-Res denies that it's involved in the new Abrams project, according to Florian Schmitt, the firm's creative director, "though I don't suppose we'd tell you if we were." Paramount and Abrams' production company Bad Robot were unavailable for comment.

The current mysterious movie trailer has the release date "1-18-08." Fans looking online found the Web site 1-18-08.com, which featured pictures of the characters in the trailer. Watching the trailer frame-by-frame, some enthusiasts noticed that one of the characters was wearing a T-shirt for Slusho, a fictional beverage that had been mentioned in "Alias." Online sleuthing led to the Web site slusho.jp, a promotional site for the nonexistent Slurpee-like drink. Records showed that the Slusho Web site was registered before the trailer aired, indicating that the site almost had to be official.

But after the initial rush of discoveries, fans began to question: Where is the rest of the game? Unforums.com, a forum devoted to alternate-reality games, features more than 6,000 posts -- which have been viewed about 400,000 times -- from players searching for clues since July 3, when the trailer first appeared before the "Transformers" movie.

If they have indeed found a "rabbithole," the fans do not know how to enter, and they're left hoping that J.J. Abrams will unleash a white rabbit to lead the way.