What Betty wants is to be a nurse; even more, she wants to be the lover of Dr. David Ravell, who happens to be her favorite character on the TV soap opera “A Reason to Love.” Director Neil LaBute (“In the Company of Men”) follows his deluded heroine as she heads for Los Angeles in a borrowed Buick to fulfill her dreams. The Buick, unfortunately, contains the money her husband’s assassins (hit-man team Morgan Freeman and Chris Rock) are determined to collect. The chase is on.

There are inspired moments in this edgy, unstable comedy, such as the scene when she meets her dream doctor at a Hollywood benefit, oblivious to the fact that he’s soap star George McCord (a wonderfully smarmy Greg Kinnear). He assumes she’s a desperate actress auditioning for a part in the show. “That is just great improv!” he says, wowed by her ability to stay in character.

Up to a point, we happily suspend our disbelief. But the script (by John C. Richards and James Flamberg) pushes its luck too far. Kinnear’s blindness to Betty’s madness goes on too long; Freeman’s obsession with the woman he’s chasing neatly parallels her romantic fantasies, but it doesn’t ring true. Swerving from viciousness to whimsy to dubious feminist fable, “Nurse Betty” doesn’t jell. Still, with a cast as charmed as this, it comes oh so close.