Jack Shephard’s (Matthew Fox) decision to put a plan in action in order to set things right on the island is met with some strong resistance by those close to him, and John Locke (Terry O’Quinn) assigns Ben Linus (Michael Emerson) a difficult task.

And here are the big spoilers from TV Guide along with a preview:

LOST Season 5 Finale we will see some “dead” characters return.
The dead will walk again in Lost’s two-hour season finale on May 13. Michael Emerson, who plays Ben Linus, tells me, “We see some people from the past. It keeps us speculating why certain people seem to be holding on and revisiting the living in some interesting ways.”
Terry O’Quinn–whose John Locke is one of the undead, says the finale will help explain why John, as well as Jack’s father, Christian, came back to life on the island. “Someone thought they’d be useful,” teases O’Quinn. “Someone is using Locke to their ends.”