The life of executed serial killer Aileen Wuornos is no stranger to the movies. Nick Broomfield’s 1992 documentary, Aileen Wuornos: The Selling of a Serial Killer, depicted an unrepentant real-life Aileen on death row and didn’t manage to engender much empathy on behalf of its subject. Broomfield instead focused on the media frenzy surrounding the case and shed more light on a couple of bizarre characters—Aileen’s public defender as well as an older Christian woman who adopted Aileen post conviction—than on Aileen herself.

Monster partially fictionalizes a few details but the essence of the tale is intact, with a narrow focus on the year prior to Wuornos’ arrest. In contrast to Broomfield’s documentary, Monster is a fully fleshed out, emotionally developed character study that’s challenging, terrifying and ultimately hopeless.

Writer-director Patty Jenkins chooses to explore the period of time from 1989-90, when near suicidal Florida highway hooker Aileen "Ly" Wuornos (Charlize Theron) walked into a gay bar and accidentally found what would become the love of her life and salvation—a questionably naïve young woman named Selby Wall (Christina Ricci), who offered, for a brief time, a chance at a better life away from the shame and pain she’d known through abuse and tricks dating back to age 13.

The film suggests that almost simultaneously, Aileen killed her first john—in self-defense and during the course of a brutal rape—and unsuccessfully vowed to get clean from the streets. Her dream was to buy Selby a house in the Florida Keys, and she was damn well determined to do it with her eye on getting a normal job and cleaning up her mess of a life. Defeated by a shot at living in the straight world, she ended up right back turning tricks and her rage led to the executions of seven men, whose wallets and cars provided the means to an end for Wall and herself.

It’s lurid subject matter, that’s for sure, and certainly not for every taste. But Jenkins wisely humanizes the love story and in collaboration with the electrifying Theron, creates a pathetic, sad, wholly believable portrait of a woman most of us would steer clear from. They find a great humanity in the character that gives the film’s inevitable climax—the disintegration of the love affair and the escalation of violence—a deep, compassionate melancholy that doesn’t forgive Wuornos for her crimes, but certainly makes us understand them.

The relationship at the heart of the film is a complex one and co-dependent, based on desperation and circumstance. Selby is looking to Aileen for security, while Aileen is desperately looking for salvation. The actresses work hard to make their scenes together tender, particularly effective in a moment set at a roller rink when they share a first kiss.

There’s more than a little complicity going on in the relationship, and though Selby isn’t explicitly aware of the murders, she certainly enjoys the money and doesn’t mind seeing her newfound love being used and abused to bring it home to her. Aileen, on the other hand, is doing all she knows how to support the one person who’s never treated her like a castoff.

Ricci, with her lovely voice and perfect enunciation, is a sweetly appealing foil to Theron’s gruff and grit. Theron nails a key scene late in the film when she explains to Ricci that she’s "a good person," and that "people die all the time."

Anyone who took notice of her dramatic chops in Taylor Hackford’s The Devil’s Advocate may have seen a glimmer of what Theron, woefully underestimated in Hollywood and pigeonholed by her angelic visage, is capable of delivering. With an extra thirty pounds, bad teeth, freckled skin and a horrid dye job, the physical transformation is nightmarish.

However, none of this would matter if Theron herself had not reached deep into some primal, animalistic place to display the level of rage and depth of sorrow Aileen Wuornos undoubtedly possessed. She’s just about unbelievable in this role, and the power she displays in the murder scenes combined with the emotionally naked protectiveness she reveals to Ricci is galvanizing.

If there’s not an Oscar nomination in the bag for Theron, it’s only because Monster is such a defiantly gutsy film, with such a dark heart that older Academy members may have a hard time looking past its unapologetic anti-heroine’s rough-hewn edges, offbeat sexuality, savage violence and bleak despair.

For the rest of us, Theron makes Monster unmissable.