Jesse Eisenberg proves that neurotic, frail-looking kids have existed in all strata of society throughout the history of mankind. And that’s a good thing, because somebody has to stand up to the bad guys, and it might as well be the apparent lightweights.

Playing an orthodox Jew in Holy Rollers, which opens today exclusively at the Angelika Dallas, Eisenberg fits right in. Directed by Kevin Asch from a script by Antonio Macia, and inspired by true events, the film begins in Brooklyn as a very righteous, innocent Sam Gold (Eisenberg) looks forward to an arranged marriage with a nice Jewish girl. He works hard with his father (Mark Ivanir), who owns a fabric business, and is quite content to toe the line.

Sam and his best friend Leon (Jason Fuchs) shake their heads in dismay and disapproval over the conduct of Leon’s older brother Yosef (Justin Bartha). Yosef looks like a Hasidic Jew, with his distinctive hair style, but he doesn’t act like one, cursing in the street and boasting openly about sex, rebellion and a very worldly lifestyle. One day Yosef comes to Sam with a proposal to make a little money by traveling to Europe and bringing back “vitamins” that will help people. On another day, Sam might have rejected Yosef outright, but his would-be wife’s family has rejected him as a potential husband, possibly because Sam’s family is not financially suitable. Tempted by the financial landfall offered by Yosef for a one-time job, Sam accepts, but only on the condition that he bring Leon.

Yosef senses that Sam is a kindred soul, ready to be lured to the dark side, but knows that his younger brother is too righteous for what he has in mind. Still, he takes them both along to Amsterdam, where the two innocents abroad are properly wide-eyed. Leon is suspicious all along, but when they return to New York and one of Yosef’s “associates” spills the beans on what they really brought home (the new and instantly popular Ecstasy pills), he is immediately outraged and walks off in a huff.

Sam, however, is delighted with the quick and easy money. So much cash! So little effort! He pretends outrage as well, to placate Leon, but is quick to volunteer his willingness to continue working with Yosef. With the hook set, Yosef starts reeling Sam into the drug trade.

Dressed in traditional garb, Sam discovers that he is never suspected by the authorities, something that Yosef has already figured out. Yosef has been recruiting Hasidics off the street to serve as mules, taking advantage of their worldly naivete, and making big money in the process. Yosef is only a middle man, though, serving as lieutenant to established neighborhood gangster Jackie Solomon (Danny A. Abeckaser). Jackie, a friendly if oily sort, is pleased with Sam’s good business sense and increasingly cool manner of dealing with, well, everyone: recruiting mules, supporting Yosef, giving Jackie negotiating tips, and keeping Jackie’s girlfriend Rachel (Ari Graynor) company when Jackie doesn’t want to bother with her.

Asch, making his feature directing debut, gives the film a congenial air while maintaining a scruffy atmosphere. Nothing that Sam or his criminal cohorts do looks glamorous; it’s a dirty business, sometimes taking place in squalid surroundings, sometimes in unwelcoming nightclubs, but the settings remain in the background. They don’t suddenly become more exciting or better looking just because a huge amount of cash is changing hands. In that way, the business dealings are treated as normal and everyday transactions, as though the players were dealing in diamonds — or fabric, like Sam’s father — rather than drugs.

Sam descends into a moral quagmire with deceptive ease, lubricated with the oil of Yosef’s charming facade. Yosef facilitates Sam’s downfall; you get the sense that he desperately needs someone to validate his own bad choices, maybe someone with a common background to keep him company in his abject misery.

As Sam, Eisenberg is something of a marvel. He may appear to be a lightweight, the friendly kid that can be pushed around with a feather, but he taps into a deep reservoir of resentment and increasing self-loathing. He’s drawn to the lifestyle, he loves the responsibility, he likes the money, he likes Jackie’s girl, yet he knows that he’s pushed away from his own moral compass and he ends up floundering.

Like most of us, he has an innate desire and need to stay within the boundaries of good personal conduct. It’s left for Sam to determine when he’s gone too far, and by then it may be too late. Eisenberg, who’s also appearing in the currently playing Solitary Man alongside Michael Douglas, gives a deft, sobering performance.

[Holy Rollers opens exclusively today at the Angelika Dallas.]