It seems pretty clear, for anyone who has watched Matthew Broderick in such movies as “The Cable Guy” or “Ferris Bueller’s Day Off,” that what he does best is happy-go-lucky with a mix of giddy-unstable. In his best roles, Mr. Broderick has succeeded in suggesting a conflict playing out in the hidden depths — a man trying to appeal to his better instincts despite the turmoil unfolding beneath the surface.

So one wonders why writer-director Peter Tolan thought Mr. Broderick would be a good fit for the dark and depressing “Finding Amanda,” a confused comedy opening on screens across the city today. He is cast here as Taylor Peters, an alcoholic screenwriter whose gambling addiction has prompted his wife to boot him out of the house. Taylor embarks on a road trip to Las Vegas, determined to win his wife back by rescuing her niece from a life of prostitution in the desert. While there, he might also find the time to squeeze in a little gambling.

From scene one, Mr. Broderick looks out of place. Taylor doesn’t so much hold himself back as operate at the emotional extremes, getting furious with his business manager, desperate with his wife, and exasperated with a casino manager (a smarmy Steve Coogan) who won’t spot him money. The more animated Mr. Broderick becomes trying to fill Taylor’s shoes, the less believable he is. It probably doesn’t help that Brittany Snow, as Taylor’s titular niece, delivers one of the year’s most vulnerable performances. The profoundly conflicted prostitute alternates between warm smiles and harsh tears, seeing prostitution as at once enabling and degrading. Once we find Amanda, the movie becomes a convincing study of a character at a crossroads. Taylor, though, comes across as more whiny than worldly.

As the plot thickens and “Finding Amanda” twists the politics of gender and addiction, part of the disconnect between Amanda and Taylor seems to be intentional. For a good while, as Taylor talks with his wife (played by a one-note Maura Tierney) in hushed whispers about her prostitute niece, “Finding Amanda” constructs an all-too-familiar dynamic of upper-class elites rushing to rescue the working-class woman in distress.

But as the days tick by in Las Vegas and Taylor continues to spend each waking hour in the casino, the balance of disorder begins to shift. Amanda may be fooling herself by rationalizing the reality of her unfortunate occupation, but it is Taylor, who loses tens of thousands of dollars on horse races, who is engaged in a far more dramatic game of denial. When Amanda meets up with him early in the film, he’s wallowing in his casino seat, sipping on soda — he prides himself on his sobriety — and imploring the horses on the big screen to run faster. But as the days drag on and we realize that Taylor’s life isn’t all that different from Amanda’s — complete with a meaningless job and a floundering relationship — it’s his flaws that come to the fore. He starts drinking, starts sampling Amanda’s drugs, starts asking the casino to up his credit line, and starts lying to his wife on the phone.

Given the bleak subject matter, it’s odd to see Mr. Tolan repeatedly push the film toward the easy punch line. Just as things start spinning out of control, “Finding Amanda” is quick to offer us diversions: Taylor pleading with the casino manager for more money, Taylor arguing with Amanda’s pimp in the back alley, etc. It doesn’t seem as if the movie really knows what it thinks of these characters, or their plight. Maybe it’s mired in a similar process of denial, refusing to think of its two main characters as the failures they are.

ssnyder@nysun.com