All the romantic comedy gloss in the world can’t save a script as stale as last week’s wedding cake. Despite a promising set-up and talented performers, it leaks air like a tire that ran over a tack.

Debra Messing (“Will and Grace”) is one of television’s all-time funniest women with impeccable timing, brilliant with both verbal and physical comedy. But she gets a lot of help on the show from the writers who created a terrifically appealing and witty character. Here, she plays Kat, an insecure and not especially interesting young woman who is in a panic over what she thinks of as two of the most terrifying words in the English language on her sister’s wedding invitation. They are: “and guest.”

Her younger sister Amy (Amy Adams) is getting married. And Kat’s ex-fiance is the best man. Kat needs a date to bring to the wedding so that “the ex-fiance will be sorry that he left you and your family will think we are in love.”

With $6000 from her retirement account, Kat hires Nick (Dermot Mulroney), a male escort she read about in the New York Times Magazine. Kat and Nick pretend to be in love to reassure the family and torture the ex. But there is an undeniable attraction between them as well.

So they tell us, anyway, which is one thing that is wrong with this movie. They describe, but they do not show. The movie wants us to find Kat adorable and endearing. She is just fluttery, self-centered, and insecure. The movie wants us to find Nick desirable. But we hear about it more than we feel it. Kat’s cousin is supposed to be delightfully outrageous. But raunchy is not the same thing as outrageous, even if a few supportive comments are tossed in, and it is especially not the same thing as delightfully outrageous. Give us something specific, people! That’s why they call it “writing.”

Then there is the troubling Pretty Woman problem of having a light romantic comedy with characters whose behavior is unsavory. This lends a sour tinge to the purported hijinks.

Most of the people behind this movie are women. They show some sensitivity to just what it is that someone like Kat would want from Nick, but, regrettably, they don’t show any more wit, insight, heart, or imagination than we find in the dozens of dull movies about female characters made by men.

Parents should know that the movie includes some strong material for a PG-13, including brief partial nudity, explicit sexual references (including prostitution, infidelity, a joke about an orgasm, the idea that “the best sex is make-up sex,” and a drunken sexual encounter that is supposed to be romantic), smoking and a lot of drinking (characters get drunk and hung over)

Families who see this movie should talk about whether it is true that people get the love life that they want. Why does it take courage to let someone love you?

Families who enjoy this movie will also enjoy Runaway Bride and French Kiss.