Following a pair of tonally lighter films (2000's "Nurse Betty," 2002's "Possession"), Neil LaBute, a writer-director more famous for exposing the bleaker, more disturbing sides of human nature (1997's "In the Company of Men," 1998's "Your Friends and Neighbors"), returns to his old stomping ground with the challenging and wordy "The Shape of Things." Originally conceived for the London stage in 2001, LaBute has transferred his four original actors (Paul Rudd, Rachel Weisz, Gretchen Mol, and Frederick Weller) for this mostly successful cinematic adaptation, and their close familiarity with their roles is apparent from minute one.

Adam (Paul Rudd) and Evelyn (Rachel Weisz) meet by chance one day at the museum where Adam works and Evelyn is about to deface a nude sculpture that has been needlessly censored with a fig leaf. Both are graduate students at Mercy College, where Evelyn is preparing her art thesis, but otherwise do not really seem suited for one another. Whereas Evelyn is outspoken and beautiful, Adam is a little pudgy around the edges and has no seeming fashion sense. Nevertheless, when Adam questions their relationship, Evelyn responds, "Don't worry about 'why' when 'what' is right in front of you." Pretty soon, as Adam begins to fall for Evelyn, he willingly takes her advice to change his physical appearance and strengthen his self-esteem. In the process, two more characters become unintentionally embroiled in their questionable relationship: Adam's engaged friends Jenny (Gretchen Mol) and Phillip (Frederick Weller).

What begins as an offbeat, rather lighthearted romance brutally segues in the second half into something far more dark and unsettling. "The Shape of Things" raises several thought-provoking topics within its quick 96 minutes, including the value of art, the importance society places on materialism and conventional beauty, and the effect one individual can have on another within a love relationship. As Adam is subtly egged on (but not forced) by Evelyn to lose weight, change his clothes and hair, and even get a nose job, Adam goes through a transformation that makes him feel better, but at the potential cost of his longtime best friend Jenny, who has loved him for years. She and fiancé Phillip are visibly jarred by Adam's changes, and wonder why someone like Evelyn would be interested in him. All of this is, indeed, a setup for a key discovery in the third act that is almost shocking in its unblinking depiction of human cruelty.

With the camera steady on long, unbroken shots, the actors are let loose to further explore their characters without the hindrance of unnecessary edits, and each one of them delivers an exceptional performance. As total opposites Adam and Evelyn (all biblical allusions intentional), Paul Rudd (1999's "200 Cigarettes") and Rachel Weisz (2003's "Confidence") are so convincing it's scary. Rudd brings such an empathetic vulnerability to his role that what happens to him in the crucial last twenty minutes is almost difficult to watch. And Weisz is alternately alluring and mystifying, perfectly embodying the headstrong Evelyn, who may or may not be exactly whom she appears. As counterparts Jenny and Phillip, Gretchen Mol (1999's "The Thirteenth Floor") and Frederick Weller (2001's "The Business of Strangers") add unusually strong support to a technically sparse film with not a single other speaking part.

As audacious as Neil LaBute's attempt to open things up is, he is not always able to overcome the notion that this started off as a stage play. With a total of only about twelve elongated scenes, the dialogue exchanges occasionally go on a little too long and feature some stilted passages, while the blocking feels slightly too stagy at certain points. This is the movie's one debit, significant enough to be mentioned but not so much that it destroys everything else that is so very good.

"The Shape of Things" is grim in its look at what one person is capable of doing to another, but it is not heartless. The characters are sympathetic without having to compromise their flaws, and the literate, knowing dialogue is oftentimes exquisite. As for the centerpiece of the film, a climactic confrontation between Adam and Evelyn, Rudd and Weisz play it to brilliant effect, and LaBute handles it with meticulous skill. The final moments are particularly heartbreaking, offering no false pretenses or easy answers even as the viewer is led to believe there may still be a glimmer of hope for these characters yet. "The Shape of Things," warts and all, is a motion picture not easy to shake.