The Mercury Players Theatre has struck green gold this fall with "Reefer Madness: The Musical," a new L.A. production that liberally expands on the cult-classic 1936 exploitation film.

With the walls of the set scrawled with newspaper headlines like "Marijuana: Weed from the Devil's Garden," the musical directed by Pete Rydberg begins in polemic style. The enigmatic "Lecturer" (Jordan Jackson) — possessing the looks and over-the-top gravitas of a young Jim Carrey — warns us about the plague that's been "creeping like a communist" over our country. The incredibly catchy title song brings us up to speed on the horrors of reefer, the "assassin of youth" that is "turning all our children into hooligans and whores." Meanwhile, zombie boy scouts and prom queens — victims of its terrible scourge — lumber about and perform dance moves brilliantly cribbed from "Thriller."

We are then introduced to 16-year-old Jimmy Harper (Jesse Fay), "a boy that's going places." He meets love interest Mary Lane (Kelly Murphy) in the midst of a difficult passage of "Romeo and Juliet." They bond through song over their love of Shakespeare, with zombie stagehands merrily swaying potted plants to their melodies.

But the narrator cuts in and ominously asks, "How can love blossom in a garden choked with weed?" Cut to the bluntly titled Reefer Den, where the red and black zootsuit-wearing, racial-slurring, woman-beating, marijuana magnate Jack Stone is desperate for a new clientele. He sneaks over to the jumping Five and Dime Diner, where Jimmy pines away for Mary and curses his lack of rhythmic coordination. As the musical's leitmotif eerily creeps in and the dance-happy youth grow turgid and glassy-eyed, Jack tells Jimmy that he knows a place where he can really learn to swing.

The choreography and costuming is brilliantly executed throughout the play. After a quick lesson in "swinging" with Sally (Callie L. N. Johnson), Jack offers Jimmy "a real smoke — reefer!" With the residents of the den chanting "suck it down for Sally!" Jimmy finally acquiesces, entering their world of lust and immorality. Jimmy is disrobed (marijuana leaves covering up objectionable areas) and tied to an enormous hookah, while the den erupts in an animalistic orgy of sexarobic choreography.

This single experience reduces Jimmy into a neurotic, leering lunatic — killing cats and dogs who send him accusatory glances, scaring Mary away and stealing his mother's fur coats so that he can "keep in the straw" for another week.

Even Jesus himself tries to intervene, coming off like a motivational speaker as he croons, "Take a hit of God instead/ Do you think you can handle the high?" As Jesus' gold hot pants blind everyone's eyes, angelic backup singers coo, "Listen to Jesus, Jimmy." Jimmy doesn't listen, however, and after running down an unfortunate Hassidic Jew he goes on the lam.

The dialogue in Act 1 consistently crackles with quotable, tossed off lines.

Sally brags, "If I can't turn [Jimmy] on, he ain't got switches," and Mary enthuses that love is "softer than a pillow stuffed with bunnies." There is even a hilarious interjection by the Lecturer that warns how Jazz musicians like Cab Calloway and Duke Ellington "are in fact agents of evil," their hopped-up music filled with "unnecessary grace notes" that invariably lead from "seducing white women to unspeakable acts of degradation." The orchestra should have attempted to live up to this description, however, as it dutifully played a tame bop beat without a lead saxophonist or trumpet. On the other hand, the songs' lyrics often risk getting too carried away with themselves. The appearance of an infant singing about how he was sold for his mother's "daily fix" was commendably ridiculous, but too much.

Unfortunately, Act 2 gets a bit mechanical, with dialogue and songs often devoid of the snappy wit that was so effortless in Act 1, instead working wholly toward the quickly progressing plot. The law's hot pursuit of Jimmy is strangely forgotten after he is enticed by Jack with a "harmless" brownie and lapses back into his old habit. At the same time, Mary is tricked into smoking some reefer at the den, turning this wholesome church girl into a whorehouse S&M slut. When she is caught by Jimmy in the middle of throes of passion, an inevitable brawl ensues, shots are fired, lovers harmonize while hemorrhaging blood and someone is framed for murder. Will killing off most of the cast, quick action by someone with a guilty conscience and a surprise presidential pardon by FDR, save the wrongly accused from getting the electric chair?

The mood suddenly shifts from trenchant irony to thinly veiled didacticism as George Washington and the Statue of Liberty join the cast for a final song that puts the play's marijuana histrionics into the context of Cold War fearmongering.

"Once the reefer has been destroyed," they blithely sing, "we'll move on to Darwin and Sigmund Freud. … The ends will justify the means." Though the sentiment is fitting, the shift in tone is pretty jarring, and a little subtlety would have gone a long way here.

The brilliance of the first act, however, more than makes up for the second act's missteps, and you'd be crazy to pass up a "homegrown" musical as deliriously inventive as this.

"Reefer Madness: The Musical" plays at Mercury Theater 8 p.m. Thursday-Saturday, with matinees at 3:30 p.m. Sept. 29 and Oct. 6, the final date.
Student tickets are $12.