Let's see if I can, without giving away too much, get to the crux of why "About Adam" self-destructs despite being quite entertaining and consistently amusing.

The movie is a buoyant but dark comedy about a conspicuously charming young grifter (Stuart Townsend, "Shooting Fish") who seduces an entire generation of one average suburban Irish family, carrying on torrid, secret affairs with all of them at the same time.

It's clever in that the same story is told in turn from each sibling's perspective and is brimming with glib wit in both dialogue and circumstance. But throughout the picture there are nagging little problems that foreshadow a 500-pound gorilla of a debacle that runs amok through the finale.

The first passage of the movie is told from the perspective of Lucy, a singing waitress with history as a heartbreaker who falls in love for the first time when she meets Adam, a charismatic customer who flirts with her in her restaurant. Problem No.1 is that Lucy is played by Kate Hudson ("Almost Famous"), a distractingly contrived casting decision clearly thrust upon director writer-director Gerard Stembridge by Miramax as a way to better market the film in America, where her star is rising fast.

Hudson's singing is badly dubbed and her Irish accent is more just a slurring of her dialogue, but other than that she's quite winning (if blatantly out-of-place) as her self-chastising internal dialogue introduces us to her family.

"About Adam" then moves on to the points of view (and narration) of her two sisters -- mousy bookworm Laura (the terrific Frances O'Connor) and unhappily married Alice (Charlotte Bradley) -- who are seduced in turn by this chameleon lover, a man who seems to be different things to every woman. They each get something out of sleeping with this guy, soon to be their sister's fiancé. Laura discovers the heart of a sexy beast's beating beneath her frumpy cardigans. Alice gets the first good sex she's had since marriage.

But this brings us to unavoidable problem No.2: Stembridge doesn't dig deeply enough into these character to explain why in this supposedly loving (if troubled) family none of Lucy's siblings would subsequently steer her away from marrying this conniving habitual cheat.

Next in the plot there's David (Alan Maher), Lucy's soccer hooligan younger brother who worships Adam like he's Elvis or The Fonz. Frustrated with living in a house full of women, he has so much admiration for a stud that can juggle them all that, yes, even he starts thinking of Adam sexually -- and boy, is he confused about it.

Adam may be confused himself, but if he is, we're not privy to it. The movie's big problem No.3 is that while Townsend is devilishly appealing in the role -- with his mysterious, almost rock star-like charisma -- his motivation for toying with this family's affections is left completely unexplored. Is he a pathological liar? Is he a con artist? What makes this guy tick? He's not a character, he's just a plot device. It turns out that "About Adam" isn't about Adam at all.

If the movie maintained its slightly bawdy edge, the humor might have pulled it through in spite of its shortcomings. But in the last act, director Stembridge really takes the movie in the wrong direction. Ignoring every ugly (yet somehow funny) thing that's happened so far, he whitewashes the fact that Adam is a total cad in the name of providing an insincere, upbeat and clandestinely misogynistic ending.

One more complaint -- a minor technical pet peeve -- just for good measure: The dialogue in some scenes is quite obviously re-recorded, and it was done so in rooms with entirely different acoustics than the rooms in which the scenes were shot. This kind of oversight is hardly momentous, but it sure is distracting.