IMAGINE AN R-RATED version of the comic strip "Cathy" -- an unoriginal, repetitive collection of jokes about irrational sexual jealousy; obsessive, if futile, dieting; the tribulations of the modern office; and the fashion faux pas of the plus-size working gal, all of which is sprinkled with liberal references to sex, drugs, alcohol, cigarettes and the f-word -- and you have a pretty good idea of what "Bridget Jones: The Edge of Reason" feels like to a nonbeliever.

By nonbeliever, of course, I mean anyone who is not a fan of author Helen Fielding's "Bridget Jones's Diary," the wildly popular book that spawned the only slightly less tiresome 2001 film to which this is a sequel. Mind you, you don't have to actively dislike the books, just never to have read them. As a result, you won't even be able to sit there and enjoy the somewhat passive pleasure of having your favorite characters, catchphrases and scenes from the page brought to life on the big screen.

Take that delight away, and there isn't much left.

"Edge of Reason" picks up where "Bridget Jones's Diary" left off, with the title character (Renee Zellweger) in the arms, er, bed, of the dashing Mark Darcy (Colin Firth). Needless to say, these stories being a kind of celebration of dysfunction, Bridget can't leave well enough alone and has soon done everything in her power to insult, unnerve, embarrass and otherwise shake the faith of her new, shagadelic boyfriend. This she accomplishes by being rude to his professional colleagues, staring at him like a psychopath while he's trying to sleep and accusing him of infidelity with his beautiful, skinny and much younger assistant, Rebecca (Jacinda Barrett). And -- hoo boy -- wait till you find out how wrong she is about that last one.

In short order, Bridget has utterly alienated Mark's affections, leading to a predictable plot twist wherein our heroine finds herself sitting in a squalid Thai prison cell after having been caught smuggling drugs.

Say what?

That's right. One minute you think you're in the funny pages, and the next thing you know it's "Midnight Express." Talk about a wrong turn. It's a far-fetched turn of events, not to mention a miscalculated tonal shift for a romantic comedy, but it's in the book, so there you have it. Naturally, the arrest is all a horrible misunderstanding, and things will soon be set right for the plucky Bridget, just as soon as Mark can be convinced that his on-again-off-again lover didn't spend a hot and heavy night in a Thai hotel room with the dastardly Daniel Cleaver (Hugh Grant). Yes, ladies, he's back, that devilishly attractive bounder who also just happens to be Mark's longtime rival for Bridget's affection, as Jones-ophiles will no doubt recall.

It's all one big, unsuccessful struggle to seem terribly, terribly lightweight, which is just what you might say about Bridget. As far as that is concerned, unfortunately, Zellweger appears not just to have gained twice as much weight as she did for the first film, but to have overindulged her character's fondness for tobacco and booze as well. The actress looks not only bloated but bleary-eyed and blotchy, as if recuperating from a weeklong bender. And it doesn't help that director Beeban Kidron spends so much time fixating on Bridget's derriere and over-large drawers that it approaches an unhealthy fetishism.

None of this is, however, what makes Bridget so unattractive. That is accomplished by Fielding herself, who, along with co-writers Andrew Davies, Richard Curtis and Adam Brooks, has turned what I can only believe were Bridget's charmingly human imperfections on the page into a lump of schoolgirl-style boy-craziness, corrosive self-loathing, addictive personality traits and neurotic insecurity, making for one singularly unbecoming character, who should, by rights, forever remain a "singleton."

BRIDGET JONES: THE EDGE OF REASON (R, 101 minutes) -- Contains obscenity, drug use and sexual content. Area theaters.

Renee Zellweger reprises her role as the neurotic singleton in "Bridget Jones: The Edge of Reason," a v. v. unsuccessful sequel to 2001's "Bridget Jones's Diary."