If you don't know what a libertine is, you could look it up in the Oxford English Dictionary ("a man who is not restrained by morality, esp. in sexual relations") or watch Johnny Depp live the definition in "The Libertine." Believe it or not, you're better off with the OED.

That's not to say that Depp doesn't have his moments as the 17th century's John Wilmot, the 2nd Earl of Rochester, one of the celebrated rakes of Restoration England and someone who was unyieldingly self-destructive before there was such a term.

Unfortunately, Depp's best moments, and the film's as well, take place in its opening sequence. Wilmot, resplendent in haughty attitude and long-haired wig, faces the camera and delivers a personal manifesto ("You will not like me; I do not want you to like me") with such confrontational bravado that it's difficult not to be impressed.

And Depp, one of the most charismatic of contemporary actors, certainly is convincing as Rochester, a handsome scoundrel who favors ruffled shirts and lives to be as amoral as possible. "Any experience of interest," he insists, "will be carried out at your own expense."

Unfortunately, as numerous movies have proved, watching a notorious debauchee debauch himself to death is not a recipe for involvement. Yes, the Restoration was an unapologetically immoral age, but seeing it happen on screen is more tiresome than engrossing.

"The Libertine" is also not helped by its creative personnel. Screenwriter Stephen Jeffreys, who adapted his own successful play, has left key scenes feeling stagebound. And Laurence Dunmore, a prominent advertising and music video director making his feature debut, has been more successful with period ambience than persuasive emotion.

The film begins in 1675, with Rochester and his young wife, Elizabeth (Rosamund Pike), being recalled to London after a few months banishment in the country. It seems that King Charles II ( John Malkovich at his most regal) has a plan for him. More delusional than most rulers, Charles suggests that Rochester write a major work of literature celebrating his reign.

The king would like the writer to be what Shakespeare was to Queen Elizabeth. Chafing at being the royal favorite, Rochester nevertheless agrees, but it's clear that the monarch has no idea what he's in for.

"The Libertine's" other narrative strand has to do with Rochester's infatuation with Elizabeth Barry (Samantha Morton), a young woman intent on being a great actress in an age when actresses were better known for questionable morals than on-stage skills. If Rochester wrote the book on "live fast, die young," Barry is the prototypical independent woman, determined to be beholden to no man. Depp and Morton are good together, but "Libertine" doesn't know how to make the most of their interactions.

With its emphasis on muddy streets, muddier language and raunchy behavior, "Libertine" is a trying experience. As we watch Rochester fall apart in spectacular fashion, it's clear that a major lure for the venturesome Depp was the chance to play a grotesque, to become a pestilent physical wreck with an artificial silver nose. There's more in that role for the actor, however, than there is for us.

*

'The Libertine'

MPAA rating: R for strong sexuality, including dialogue, violence and language

Times guidelines: Graphic sexual activity, nudity, coarse language

Released by the Weinstein Co. Director Laurence Dunmore. Producers Lianne Halfon, John Malkovich, Russell Smith. Screenplay Stephen Jeffreys. Cinematographer Alexander Melman. Editor Jill Bilcock. Costumes Dien Van Straalen. Music Michael Nyman. Production design Ben Van Os. Running time: 1 hour, 50 minutes.

In limited release.