Toe-tapping melodies and hack-and-slash gore make for a surprisingly successful marriage in “Repo! The Genetic Opera.” The latest offering from famed horror director Darren Lynn Bousman was screened Friday in Park Auditorium, weeks before its theatrical release Nov. 7.

“Repo!” transports its audience to a futuristic world consumed by chaos after a global epidemic of organ failures. Desperate for salvation, the dying public turns to GeneCo, a multibillion-dollar company that specializes in organ transplants. But if clients can’t afford to keep up with the company’s strict payment plan, GeneCo sends an assassin known as the Repo Man to kill them and collect the organs in question.

Seventeen-year-old Shilo Wallace (Alexa Vega) is unaware that her father Nathan (Anthony Head) is secretly GeneCo’s dreaded Repo Man. Diagnosed with a blood disease as a child, Shilo has been confined to her bedroom for most of her life. Her curiosity about the outside world increases as she gets older, and her eventual pursuit of it lands her in more danger than she can handle.

Head’s portrayal of the tormented Repo Man is impressive — anyone familiar with the musical episode of “Buffy the Vampire Slayer” knows that Head’s voice can move mountains — but it is Vega who delivers the most surprising performance in the film.

Best known for playing a pint-sized secret agent in the “Spy Kids” series, Vega takes on a decidedly darker role in “Repo!” She’s angsty, she’s edgy and she isn’t afraid to drop a few f-bombs. Her transformation from Disney clone to rock ‘n’ roll bad girl is made official during the song “Seventeen,” which includes one of Shilo’s most memorable lines: “Daddy’s girl’s a f------g monster!”

Paris Hilton also turns out an enjoyable performance as Amber Sweet, the plastic surgery-addicted daughter of GeneCo president Rotti Largo (Paul Sorvino). Her breathy vocals and exaggerated sexuality allow her to slip comfortably into the role of the spoiled diva. While she may not be able to carry an entire film by herself — the mere mention of her role in “The Hottie & the Nottie” still makes many reviewers cringe — her performance in “Repo!” proves that she can hold her own as a supporting character.

At the center of all the drama is the mysterious Blind Mag (Sarah Brightman), an opera singer who performs exclusively for GeneCo-sponsored concerts called “genetic operas.”

Brightman, a Broadway legend,  is a refreshing addition to the cast. Her operatic vocals juxtaposed with the film’s rock-heavy score result in something pulled from an Evanescence album — and that’s a good thing.

The characters’ backstories are cleverly revealed through a series of comic book-style animations, giving the audience a fuller understanding of how the characters are connected and why they clash with one another. The tension between the characters becomes more palpable with each interaction, eventually culminating in a dramatic showdown at the ominous opera. When the ill-fated night arrives, the characters combine their voices for “At the Opera Tonight,” a song that oozes anticipation in the style of “Tonight” from “West Side Story” or “One Day More” from “Les Misérables.”

Aside from its genius soundtrack, the film’s most impressive feat is that it effectively straddles the horror and musical genres, remaining equally faithful to both. Almost every musical number contains a special treat for the film’s bloodthirsty audience. During one song, Nathan slices open a man’s stomach, grabs his insides and uses him as a human puppet. The resulting duet is pretty spectacular.

“Repo!” is already being hailed as an instant cult classic, and some are even referring to the film as the next “Rocky Horror Picture Show.” While it’s probably too soon to be jumping to those conclusions, it’s safe to say that “Repo!” will connect with a specific audience — the type of people who enjoy watching “Grease,” but strongly believe that a few dead Pink Ladies would really jazz up “Beauty School Dropout.”

“Repo! The Genetic Opera” was written by Darren Smith and Terrance Zdunich, and directed by Darren Lynn Bousman.