Based on the novel by Susanna Moore, "In the Cut" is a fascinating psychological character study wrapped in a murder mystery where the identity of the villain hardly seems to be the point. Although it will likely displease and bewilder filmgoers used to the more conventional side of cinematic thrillers, it holds so much depth, so much innovation, and such a crystal-clear vision of what its intentions are, that more learned film buffs are in for a treat. And, as written and directed by Jane Campion (1993's "The Piano"), "In the Cut" is pitch-black in its tone and admirably uncompromising in its character portrayals and narrative details. It is easily one of the most haunting—and best—motion pictures of the year.

In a startling change from her usual frothy romantic comedies, Meg Ryan (2001's "Kate & Leopold") has delivered the kind of powerful, three-dimensional, courageous performance that expands and strengthens careers (think Nicole Kidman, who produces here). Ryan has gotten much publicity for baring it all here, and that she does, but what is so very astonishing and risqué about her Oscar-worthy turn has nothing to do with nudity.

In her portrayal of English professor Frannie Thorstin, Meg Ryan has shed her blonde hair and perky demeanor for a faded brown mop and an imploding personality whose stark realism cuts right to the bone. Frannie, an intelligent lover of words, discovers at the most seemingly inopportune time in her life that she has a sexual hunger that has gone unsatisfied for too long. After witnessing a man in shadow receiving oral gratification in the basement of a New York City bar, Frannie's pent-up sex drive gets a sudden fetishistic jump-start of its own. Unfortunately, her attraction toward Detective Giovanni Malloy (Mark Ruffalo) surfaces just as his investigation into a local serial killer—parts of whose latest victim were found in Frannie's garden—leads him to her. As the killer threatens to strike again, Frannie embarks on an exceedingly dangerous carnal relationship with Malloy, despite her better judgment and the rising suspicion that the psychopath in question may very well be him.

What Meg Ryan has done in her complex, demanding role of Frannie is not a cheap ploy to be taken seriously as an actress. If such an achievement occurs, more power to her. What Ryan has really done, however, is created a true-to-life, flawed character, and done it flawlessly. Her Frannie is not naive; she recognizes that her sexual dealings are unhealthy and her relationship with Malloy is inappropriate, but she gains a sort of carnal satisfaction and internal strength from her own discovered masochism that is difficult for her to give up. In what looks to have been emotionally draining, Meg Ryan gives one of the year's most brilliantly fascinating performances.

And for writer-director Jane Campion, she has crafted a challenging piece of work that falls somewhere between art and entertainment, while garnering the right to be both. Along with top-notch cinematographer Dion Beebe (2002's "Chicago"), Campion evokes a dreamlike quality to the proceedings as Frannie delves into matters she is inexperienced in and unsure about, but that may have serious, life-changing repercussions. The camerawork, intentionally jittery and seemingly at a constant struggle to capture focus, effectively foreshadows Frannie's personal journey, and aids in the uncomfortable atmosphere. Moments of symbolism, including a recurring running bystander on the street, a bride with a cast on her arm, and wordless black-and-white flashbacks to Frannie's parents ice-skating on the day they got engaged, avoid pretentiousness and rely on the power of their indelible images and the subtlety in getting their existential purposes across.

The meticulously chosen music also plays a major role in the film, opening with a wistful version of "Que Sera Sera" that acts as a cogent contrast for what is to follow. A beautifully written and acted sequence between Frannie and close half-sister Pauline (Jennifer Jason Leigh) garners even more humanistic weight with the use of Annie Lennox's "Waiting in Vain." And the way in which "I Think I Love You" plays a disturbing role in a despairing scene near the end is downright ingenious.

Enriching Meg Ryan's startling work even more is the support she gets from two other superb performances by Mark Ruffalo (2003's "View from the Top") and Jennifer Jason Leigh (2002's "Road to Perdition"). As Detective Malloy, Ruffalo hits every note perfectly in creating the right balance between suave, seductive coolness and a more threatening underlying side. Leigh brings sympathy and a quiet mournfulness to Pauline, whose desperate attempts to find her one true love has gotten stalking charges put on her.

Although the identity of the killer is unveiled at the climax of "In the Cut," it almost comes as a sidebar to the real conflict facing Frannie, whose life has spiraled out of control as a result of her quest for sexual fulfillment and a need for personal purpose in her everyday life. Throughout the film, Frannie gains further satisfaction by reading the poetry postings on the walls of the subway car. What starts as a hobby, however, gradually becomes a statement as the lines become intermingled with what is occurring in her own life. It is just another lovely little detail in a motion picture rich with ideas, exact characterizations, and visual artistry. "In the Cut" is a major cinematic achievement—simultaneously heartbreaking, frightening, unpredictable, sexy, grim, provocative and eerily plausible.