MRS. SOFFEL" is state-of-the-art melodrama -- the kind of tragically romantic movie that seems likely to induce days of heavy sighs and nights of pillow- hugging in a certain type of person.

That includes most of us, I suspect.

Diane Keaton is Kate Soffel, the neurasthenic wife of a Pittsburgh prison warden. Though she finds release in comforting the prisoners with Bibles and blankets, Mrs. Soffel feels vaguely unfulfilled -- until she meets the notorious Biddle Brothers, condemned to hang for murder. Slowly, she finds herself succumbing to the sinister glamor of older brother Ed Biddle, played by Mel Gibson, who, with his bruised and beaten mug, is even more criminally handsome than usual.

Australian director Gillian Armstrong ("My Brilliant Career") slowly and expertly orchestrates the tension as Biddle cunningly woos Mrs. Soffel and romances her into helping him and his brother escape. But Mrs. Soffel has touched something in big bad Biddle -- he impetuously returns for her, and she runs off with him in her nightgown in a midnight blizzard. The movie's emotional crux lies in Kate Soffel's realization of the finality of her decision -- when she makes the jump from mom to moll, she knows can never go home again.

"Mrs. Soffel," based on a true story, is the sensational stuff of juicy pulp romance. But Armstrong maintains a firm grip on the emotions and the camera, which makes the giddy joy of Mrs. Soffel's escape all the more elating.

Evoking the bone-chilling feel of wintry 1901 Pittsburgh, Russell Boyd's brilliant cinematography sets the bleak and blue tones of the prison and beyond against the warm, wan glow of the Soffels' home.

Gibson is terrific, and he goes beyond his boyish hunk persona to deliver rough edges and a controlled menace we haven't seen from him before.

But it's Keaton's movie, and this performance may be her most disciplined yet. No trace of ditsy Annie Hall remains: Her Kate Soffel is purposeful, even grim, and when Keaton is silent for long stretches, you can practically see her thoughts. Keaton allows herself to look careworn for much of the film, holding her beauty in reserve; when she finally uncorsets her emotions and surrenders to unfamiliar passion, her face is transformed, radiant and youthful.

MRS. SOFFEL (PG-13) -- At area theaters.