"Nurse Betty" is a skewed fairy tale, a loopy road movie that shifts in tone from whimsical to soothing to shocking and back again. With a (mostly) crackerjack cast and a plot that zags every time you expect it to zig, the production is a welcome relief after weeks and weeks of lousy flicks.

The story, which earned John C. Richards and James Flamberg a Best Screenplay award at this year's Cannes Film Festival, chronicles a pivotal period in the life of Betty (Renee Zellweger), a coffee shop waitress and ardent soap opera fan in Fair Oaks, Kansas. Although her smarmy car-salesman husband, Del (Aaron Eckhart), has forgotten her birthday, Betty plans to celebrate in style, borrowing a car from her hubby's lot for a night on the town with a girlfriend.

But matters go terribly wrong. After watching a tape of her favorite serial, "A Reason to Love," and swooning when the show's most popular character, Dr. David Ravell (Greg Kinnear) intones "I know there's someone special out there for me," Betty glances into her living room and witnesses a horrific sight. Husband Del is frantically negotiating with hit men Charlie (Morgan Freeman) and Wesley (Chris Rock), when an ugly exchange leads his being scalped and then shot to death (sensitive viewers should be ready to avert their eyes several times during the film). The shock throws Betty into a fugue state, marked by a combination of amnesia and physical fright. The suddenly psychotic woman, who always dreamed of being a nurse, hops into the 1997 Buick LaSabre and heads towards Los Angeles for a romantic "reunion" with her beloved Dr. Ravell.

Among the many things Betty doesn't know is that the car's trunk holds the very cache of drugs that prompted Del's visit from the hit men. Charlie and Wesley set out after Betty, determined to recover the narcotics and wipe out the witness to their work.

"Nurse Betty" is one of those rare films able to reference numerous other movies ("The Wizard of Oz," "Thelma and Louise" "The Purple Rose of Cairo," "Being There" and "Pulp Fiction," to name but a few), while still feeling like a true original. LaBute, whose previous movies were marked by inventive, but minimalist camera movements, proves adroit at fluid filmmaking. As always, he brings out the best from his performers.

Renee Zellweger, so terrific in "Jerry Maguire," does her best work to date here, making a remarkably smooth transition from sweet, mousy housewife to whacked-out adventurer. But her best moments come when the fugue state cracks, plunging the woman into an alien reality. Despite her massive, understandable confusion, she displays a grand air of strength and personal resolve while sorting things out.

Morgan Freeman is equally impressive as senior hit man Charlie. Freeman, one of the best actors working today, creates a complex persona that somehow manages to remain sympathetic despite his deadly occupation. Greg Kinnear is solid and likable in the dual roles of a soap opera character and a "real life" actor, while the wonderful Allison Janney gracefully steals scenes as the producer of "A Reason to Love."

On the down side, Aaron Eckhart is wasted in a brief, cartoonish turn as Betty's piggish husband. Eckhart, who starred in both of LaBute's other films and won a wide audience as Julia Roberts' boyfriend in "Erin Brokovich," deserves more than a glorified cameo appearance. And then there's Chris Rock. Yes, I know he has legions of fans. Yes, his abrasive behavior fits that of junior assassin Wesley. But Rock's loud, whiny style is pure, fingernails-on-the-blackboard annoying to me. I look forward to the day when he becomes seasoned enough to deliver his high quality jokes in a less screechy fashion.

Still, "Nurse Betty" is a corker. The highlight of the film is unquestionably Betty's cocktail party exchange with key members of "A Reason to Love," where her psychosis is mistaken as a Method Acting audition, but what happens soon after is even more admirable. I won't spoil it for you. Suffice to say that the screenwriters recognized the perfect moment for Betty's fugue state to end, allowing her journey to move from fantasy to substance. Following a summer where most film characters were depicted spinning in circles, it's gratifying to watch someone grow as a person. It's gratifying to watch the enormously gifted Neil Labute's filmmaking growth as well.