IF YOU'VE SEEN THE TRAILER for "Wicker Park," in which actress Rose Byrne seems to be stalking Josh Hartnett, you'll be forgiven for thinking it's a taut psychological thriller about romantic obsession along the lines of "Single White Female" or "Fatal Attraction." What it really is is a limp and exceedingly uninvolving melodrama about -- gasp! -- a series of unfortunate miscommunications.

Yup. There would be no movie here -- none -- if the characters in it (and here I'm talking about the normal ones, not Byrne's wild-eyed psycho) simply had answering machines, functioning cell phones, knew how to look someone up in the phone book and delivered messages to their best friends when they said they would instead of waiting until the last minute. In other words, if they acted like you and I do.

Somebody needs to be slapped here, and it's probably director Paul McGuigan and writer Brandon Boyce, who ostensibly based his screenplay on a French film called "The Apartment," but who appears to have based the behavior of his characters on something other than minimally considerate human beings.

Who, other than the Unabomber, doesn't own an answering machine?

Luke (Matthew Lillard) apparently doesn't, despite owning a successful Chicago shoe store, for which he even has business cards. Luke is the best friend of Matthew (Hartnett), an advertising photographer who's about to get married, until he stumbles across someone he thinks is Lisa (Diane Kruger), the old love of his life, a woman who disappeared mysteriously without so much as a "Dear John" letter two years ago.

The problem is, when he tracks Lisa down, he finds not the woman he remembers but a woman (Byrne) who calls herself Lisa, wears Lisa's old coat and seems to have Lisa's shoes in her apartment.

What an eerie coincidence. Naturally, they have sex.

At this point, anyone with a brain wouldn't be sleeping with the nut-job, but calling directory assistance or hitting Google to see if Lisa was still around. But no. Matthew, apparently, isn't that smart (and here I have to give credit to McGuigan for casting Hartnett, who, behind the face of a pretty 12-year-old boy, seems to be a couple of bricks shy of a load).

Where the movie collapses from the weight of its own stupidity, however, is when it reveals to the audience just how everyone's wires got crossed in the first place. And at that point it ceases to be a thriller (let alone much of a mystery), and becomes a soggy, improbable love story you can't wait to be over.

Even Byrne never really carries much danger, coming across as dumb rather than unhinged. Her character therefore is sad, not scary.

Which still doesn't explain all the tittering I heard at a recent screening. Never a good sign in a movie that's supposed to give you the creeps, not the giggles.

WICKER PARK (PG-13, 115 minutes) -- Contains obscenity and sensuality. Area theaters.

Matthew (Josh Hartnett) gazes at a woman he believes is his long-lost love (Rose Byrne, onscreen). Unfortunately he is confused -- a confusion normal people would have resolved with a call to directory assistance or a visit to Google. But then there'd be no "Wicker Park."