Charlize Theron as Aileen Wuornos: willowy beauty transforms into notorious serial killer.

he vampy starlet willing to warp her appearance for a film role is turning heads in Hollywood again.

Last year it was Nicole Kidman as the prominent-nosed Virginia Woolf in "The Hours." Before that it was Hilary Swank as the transgendered hunk in "Boys Don't Cry." Now we have Charlize Theron playing a scuzzy, down-on-her-luck murderess in "Monster."

We've heard about Theron's remarkable metamorphosis – 25 extra pounds, teased hair, heavy dentures, dark contact lenses and freckled latex mask. Makeup artist Toni G. did a spectacular job of transforming the willowy beauty into the likeness of notorious serial killer and part-time prostitute Aileen "Lee" Wuornos, who was executed in 2002 for the murder of six men in Florida.

But it takes more than makeup and prosthetics to be able to dive headfirst into the body and soul of someone we'd probably cross the street to avoid. What Theron does in "Monster" is a courageous and controlled craft. She doesn't just "play" a rangy serial killer; she totally embodies a character we can neither approve of nor turn away from. With her spastic fear, explosive rage, occasional hope and acute vulnerability, Lee Wuornos demands our attention and, most surprisingly, our compassion.

This is a performance that seems to ask: Aren't serial killers people, too?

The real Wuornos was scarier and crazier than Theron's rendition, though not by much. I first saw her in Nick Broomfield's 1992 documentary, "Aileen Wuornos: The Selling of a Serial Killer." (Broomfield co-directed another documentary, "Aileen: Life and Death of a Serial Killer," which is now playing in limited release.)

In the documentaries, she appears as a wild woman made foul and volatile by a deplorable life. Her complexion is fraught and scarred. Her eyes bulge out of their sockets. Years of tension have pulled the corners of her mouth into a nasty scowl. Although her wrists and ankles are cuffed, her entire body seems to rock and twitch as if possessed. During her 1992 trial, we see her explode at the judge and hiss at jurors that she hoped their daughters would get raped. Broomfield follows his subject with a vigilance reserved for someone who might strike without provocation.

Shake the question: What happened here?

Patty Jenkins, who wrote and directed "Monster," noticed something else.

"Her eyes weren't the blank orbs of the cold and enigmatic," Jenkins reflects in an interview. "They were terrified. As I watched her sit in the courtroom, sobbing into her lap while the love of her life testified against her, I couldn't shake the question – What happened here?"

In "Monster," Jenkins tries to get at the heart of what made Wuornos tick. The approach is mostly unbiased and devoid of tabloid exploitation. Jenkins isn't interested in justifying the crimes and punishment of Wuornos. Her goal is to explore the humanity of someone capable of committing such cruelty, without excusing the acts. In her level tone, she encourages us to take a long, objective look.

For the most part, the storytelling is plain and straightforward.

We're introduced to Wuornos as she contemplates suicide under a freeway overpass. The backdrop is wet and dreary. She twirls a gun around her finger. We've already gotten the impression that she's had it rough.

But Jenkins is careful not to make her into a pitiable victim. We get the point in a few nonindulgent flashback shots: A young Lee holding her shadowed face in her hands; a teen-aged Lee pulling her shirt up for the neighborhood boys in exchange for a few dollars; an older Lee giving a reluctant blow-job to a guy in a car. Even the dreamy voice-over declaring cheap hopes of being discovered "like Marilyn Monroe at a soda fountain" sounds more apathetic than self-pitying.

Ricci and Theron: texture and gravity.

Instead of killing herself, Lee spends her last five bucks on cheap beer at a neon-lit lesbian bar. There she meets Selby Wall (Christina Ricci), a timid suburban outcast, whose too-wide eyes suggest a child's cartoonish naiveté.

The two spar and flirt until they're wasted. Then Selby asks Lee if she wants to spend the night. Her approach is tentative. It's as if she's trying to coax a feral animal into eating out of her hand. "You don't have to do anything," she promises. We learn that Selby's been shipped to Florida to live with her bible-banging aunt as punishment for kissing a girl.

Ricci isn't given enough credit in a role that adds texture and emotional gravity to Theron's Lee. But Ricci, best known for her more assertive, stand-alone roles in "The Opposite of Sex" and "The Addams Family," brings a bright profundity to Selby.

Both actresses work like two primary colors that have been paired together to complement an entire room. There's a scene where Selby and Lee share a tiny twin bed decorated with a plaid-print bedspread. Both of them look like awkward, oversized teen-agers who can't believe they're sleeping together. Selby reaches for Lee's face with overt tenderness and whispers, "You're so pretty." The comment seems to have been lifted from someone's generic, supersaturated daydream.

As Selby and Lee: like awkward, oversized teen-agers.

But because the scene is so self-aware and the actresses so subtle, it succeeds in drawing us into the relationship. Later, when we see Lee nervously fiddling with the mailbox as the two make plans to hook up, we believe that she's probably never experienced this kind of affection.

As the film progresses, disaster erupts in an ugly, deliberate way. Lee, an itinerant hooker, is brutally tortured by a slurring, psychotic "John" (Lee Tergesen), who intends to kill her.

Jenkins preserves the horror of the attack without sensationalizing. The scene is neither too bloody nor explicitly observed. The camera lingers on Lee's face, then jump-cuts to Selby, who's waiting for her on a curbside. When Lee manages to shoot her perpetrator in self-defense, her howl of victory can be heard as a devastating realization of all the abuses heaped upon her.

The subsequent murders have a very different mood and style.

At times, Lee is portrayed as killing men in a paranoid response to the wrongs done against her. Even when the men have been passive or kind, she convinces herself that they're child molesters, potential perpetrators or witnesses. Moreover, she needs their money because she's unable to get a straight job due to her lack of skills.

Jenkins does not let Lee off the hook. Each victim is given a three-dimensional vibrancy that allows us to care about his life, and recognize the senselessness of his death. This is especially true of the final victim (played by Scott Wilson), who pleads for his life. He has a wife, children. He only wanted to give Lee a ride to someplace safe.

Jenkins sticks as close to Lee and Selby as possible without sentimentalizing their relationship.

Unwritten casting rule: hiring hot to play ugly.

As the women warm up to each other, we begin to see what motivates Lee to continue hooking, killing and robbing. These two need each other in the desperate, fumbling way of infants. Although Lee probably isn't gay, she responds to Selby's attention, and Selby grows to depend on her.

There are plenty of scenes where we see them riding around in stolen cars, grinning like star-struck lovers and hopping from one seedy motel to the next. Lee lights Selby's cigarettes, shows her off in bars and throws money at her for beer, food and carousel rides. Sometimes they squabble like brats when one thinks the other is treating her unfairly. They make up, too, but not in reasonable, romantic ways.

Their relationship is more sloppy and co-dependent. It looks uncomfortable. Selby is too passive and insecure to make appropriate decisions, so when the relationship dissolves into a kind of frenzied hit-and-run, she blinks incredulously with those big brown eyes all the way to the end of the film.

A friend of mine recently asked: If Aileen Wuornos were played by a homely actress, would "Monster" still have gotten so much hype? I'm not so sure it would've. This has a lot to do with our interest in esthetics and a belief that beauty, when not preserved, can be fleeting, malleable, finite or lost behind a mask.

There's probably an unwritten casting rule that goes something like this: You can hire someone "hot" to play someone "ugly," but you can't hire "ugly" and make them "hot."

Inevitably, there will be people who watch "Monster" and spend the majority of their time looking for the shy grin or flutter of eyelids that hint at the dazzling Charlize Theron from "The Italian Job" or "2 Days in the Valley." They can't believe this is the same actress, so they're looking for clues. Once they find her, their relief is palpable. "There she is," they whisper, "I saw her."

It's as if they've glimpsed something so charmed and supernatural that her character's unattractiveness is rendered innocuous. They chalk up the extra weight, stained teeth and shabby complexion to cinema sleight of hand. And Theron is praised for eschewing vanity (no one wants to be a narcissist), while devoting herself to a great performance.

When I walked out of the theater, feeling quiet and disoriented, I wasn't interested in how Charlize Theron "became" Aileen Wuornos.

I kept thinking of a scene where Lee and Selby have their first date at the roller-skating rink. Journey's "Don't Stop Believin'" is playing on the jukebox. Lee is holding Selby's elbow as they awkwardly dance and shuffle on skates. "I love this song," she says.

We know that bad things are going to happen, but for this moment Lee is radiantly happy. We sense an unguarded openness in her lumbering posture.

It's as if her body is reflecting rather than shielding her, and we know we're not going to see that again. The poignancy makes her shine. I've had it on my mind for days.