Jack Black shines in this Netflix comedy with a hook that rings completely false.

Every so often Hollywood cranks out a cautionary tale about the American Dream.

Sure, that dream looks good on paper. In reality, It’s a tease that traps unfortunate souls. Take Jan Lewan, the Pennsylvania polka purist whose hunger for that dream curdled bigly. He ended up spending time behind bars for his Ponzi scheme shortcut.

“The Polka King” brings Jan’s twisted tale to Netflix. The original film coasts on its star’s charm (and pipes). Look closer, and you’ll see a sermon sending a seriously toxic message.

Jack Black stars as Lewan, a charismatic singer who craved more money than what a touring polka player earns. So he got creative. He began collecting money from elderly fans with the promise of huge returns on their investment.

How? He doesn’t really say, nor does the movie. The latter is a sizable flaw, even in a comedy.

FAST FACT: The real Jan Lewan isn’t bitter to see his tragic life transformed into a Netflix movie. In fact, he told a Pennsylvania news station he harbors no ill will about the film.

Lewan’s scheme draws the attention of an SEC officer (J.B. Smoove) who tells him bluntly he’s breaking the law. That doesn’t stop Lewan, who builds a small empire on the backs of his suckers.

Those suckers are personified by an elderly couple he reels in and won’t let go. Sure, they’re naive, but they’re sinking thousands into Lewan’s scam. And he never flashes an ounce of sympathy or regret.

Not once. Yet “The Polka King” wants us to cheer him on all the same.

Part of that is Black’s fault. He’s so lovable here, so full of unbridled joy, that you want to see him succeed. And his voice, showcased previously via his rock parody duo Tenacious D, makes those polka classics pop.

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The jokes here are never big, but they bubble up all the same. Credit Jacki Weaver as Lewan’s skeptical mother in law. Lewan’s musical sidekick Mickey (Jason Schwartzman) adds little to the presentation, alas.

Jenny Slate fares better as Lewan’s wife, but she’s torpedoed by a subplot that erupts out of nowhere and feels hopelessly fake – even though it actually happened.

What movies like “The Polka King” miss is the grit behind the American Dream. Sure, the Polish emigre works tirelessly to get rich. But a wise American understands some roads aren’t paved with gold. If Plan A doesn’t reveal that elusive dream, it’s on to Plan B, C or D.

There’s nothing wrong with a cautionary tale like “The Polka King.” The American Dream can take it. The problem arises when the film asks us to forgive its monumentally flawed hero.

HiT or Miss: “The Polka King” sporadically entertains thanks to a killer lead turn. What a shame that it packs such a seriously misguided lesson.