NEW YORK » ABC's “;Lost”; returns for its fifth season tomorrow with a continuation of the lingering mysteries that make the drama such a mind bender.

The series began in 2004 with a plane crash on a mysterious island, rolling out a man-hungry smoke monster, displaced polar bear and unfriendly natives called “;The Others,”; among other oddities. As the show's cast and mythology expanded, there were romances, rivalries, kidnappings, murders, attempts to escape and a character's emotional journey through time (see the standout Season 4 episode “;The Constant”;).

Season 4 ended last May with some of the castaways fleeing the island while others were left behind—or died. The fifth season opens tomorrow night on KITV/ABC at 8 p.m. with unresolved mysteries and more question marks.

WHAT HAPPENED TO THE ISLAND?

In the Season 4 finale, “;Other”; boss Ben (Michael Emerson) turned a frozen wheel and—poof!—made the island disappear, along with Sawyer (Josh Holloway), Locke (Terry O'Quinn), Juliet (Elizabeth Mitchell) and other “;Lost”;-aways; the Oceanic Six fled on a helicopter. Ben—landing in North Africa—aimed to protect the island from arch nemesis Charles Widmore (Alan Dale), who seeks to control it. The show has been exploring the space-time continuum, and that theme will be heightened this season in the search for the island.

WHO THE HECK IS JACOB?

We've never seen Jacob, though he seems to be the all-knowing island messiah. The shadowy character lives in a creaky cabin that moves around a lot, hates technology and has communicated to the Others through Ben. Last season, Ben brought Locke to the cabin; Locke could not see Jacob, but heard him say, “;Help me.”; After Widmore's men stormed the barracks, Ben and Locke visited Jacob again—this time, Jacob spoke to Locke through a representative, Jack's ghost-daddy Christian (John Terry), who said to move the island. Ben, sensing that he'd been replaced by Locke, did the deed and peaced out.

As far as we can tell, Jacob has unknown powers, dead people for friends and a cabin fever that keeps him locked in. Online theories abound: Is Jacob an ancient supercomputer, a divine entity, a superhuman being? Expect the unexpected, and expect to see more of him this season.

HOW DOES LOCKE BECOME BENTHAM?

The cliffhanger revealed that Locke was “;Jeremy Bentham.”; Under that alias, he apparently died after visiting Jack and some others who left the island with troubling news: They need go back. While visiting Locke's casket, a cryptic Ben tells Jack they must rally his fellow crash survivors—and return with Locke's lifeless body. Lucky for Jack, Ben always has a secret plan. Emerson tells New York magazine his bug-eyed alter ego will “;carry on what seems to be his calling or his life's work or his war, whatever it is—I'm not sure exactly what it is.”; But it includes orchestrating a survivors' reunion.

WHAT'S GOING ON WITH WIDMORE AND BEN?

Widmore is the wealthy industrialist who staged the fake plane crash of Oceanic 815 and ordered a team of mercenaries on a mission to find the island and kill everyone on it. Widmore and Ben appear to have a deep-seated rivalry, deepened further after Widmore's agents murdered Ben's daughter in cold blood. Off the island, Ben recruited Oceanic Six survivor Sayid (Naveen Andrews) as an assassin; he also dropped by Widmore's home in the wee hours, vowing to kill his daughter as revenge.

Whatever game they're playing, it has rules—and Ben says Widmore has broken them. One possible rule: Widmore and Ben cannot kill each other. That would be a very Harry Potter/Voldemort-esque plot twist.

WHAT HAPPENED TO CLAIRE, JIN AND MICHAEL?

Claire (Emilie de Ravin), who we recently learned is Jack's half sister, seemed to survive a house fire—but then things got weird. She walked off in the jungle with her (un)dead father, Christian. The next time we see them, she's in the shack with Jacob, acting creepy.

As for Jin (Daniel Dae Kim) and Michael (Harold Perrineau), they presumably died on the freighter when it exploded. In an earlier flash-forward, Jin's wife, Sun, was shown at his memorial in Korea.

Some bloggers speculate he'll turn up in early episodes, dead or alive, this season. If he perished in the blast, maybe we'll see him cavorting with Jacob, Christian and other ghost people.