Mel Gibson is back, and as obsessively nuts as ever, in "Edge of Darkness" -- a manic-depressive thriller that's as entertainingly crazy as its star.

Gibson plays Boston homicide detective Thomas Craven, an old-school cop who singlehandedly raised his daughter Emma (Bojana Novakovic), who's now an MIT grad and an intern at a major defense contractor. When Emma comes home for a weekend, Thomas suspects something wrong -- especially when Emma starts developing nosebleeds and profuse vomiting.

Then, on the family's front porch, somebody kills Emma with a shotgun blast. At first, Thomas's cop colleagues think he was the target. But as he investigates, Thomas uncovers a large conspiracy involving a U.S. senator (Damian Young) and the oily CEO (Danny Huston) at Emma's company.

While pursuing Emma's killers, Thomas also garners the attention of a mysterious "fixer," Jedburgh, played by Ray Winstone ("Sexy Beast"). Jedburgh is the too-good-to-be-true character that populates potboilers like this one, a wine connoisseur who quotes poetry while attaching the silencer to his pistol. (Winstone seems a far cry, though, from Joe Don Baker, who played the role in the 1985 British TV miniseries from which this movie is adapted.)

Writers William Monahan and Andrew Bovell have experience with police procedurals like this, having written, respectively, "The Departed" and the great Aussie thriller "Lantana." Here, they appear to have worn through the pages of their English-to-Raymond Chandler dictionaries.

Take, for example, Craven's warning to the senator about a possible corruption scandal: "You had better decide whether you're hangin' on the cross or bangin' in the nails." (It always goes back to the Crucifixion for Gibson, doesn't it?)

Director Martin Campbell ("Casino Royale") stages some nifty action sequences, but he has more trouble with the moments of pathos where Craven reminisces about his dead daughter.

The whole thing kind of crashes and burns in the final 30 minutes, as Gibson turns into full-blown "Lethal Weapon" histrionics and the plot goes off the rails with him. But for a while, "Edge of Darkness" keeps viewers enjoyably on the edge of their seats.

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