Fonzie is fabulous, but the current Broadway Series South production of Happy Days — A New Musical fails to capture the warm, fuzzy feeling of the classic 1974-84 ABC television series, which offered a nostalgic view of family life in the Fifties. The less-than-stellar script by “Happy Days” creator Garry Marshall is the chief culprit, but the lackluster score by “Evergreen,” “Rainy Days and Mondays,” and “We’ve Only Just Begun” songwriter Paul Williams bears much of the blame. Indeed, the original “Happy Days” theme song by Norman Gimbel and Charles Fox, sampled throughout the show, is by far the catchiest tune in Happy Days.

Since the 1977 episode of “Happy Days” in which Fonzie — incongruously wearing his trademark leather jacket with his swimsuit—took the absurd risk of jumping a shark on water skis, the phrase “jumping the shark” has become synonymous with television series whose creative wells have run dry. That phrase also applies to musicals with paper-thin plots. In this musical-theater version of Happy Days, the hood-turned-hero Fonzie (the super-cool Joey Sorge) suffers a Dark Night of the Soul when a secret knee injury prevents him from wrestling the infamous Malachi Brothers (Matt Merchant as Myron “Count” Malachi and Jeff Sumner as Jumpy Malachi) to raise the money necessary to save Arnold’s Drive-In from greedy real-estate developers who want to demolish the beloved malt shop and teenage hangout and replace it with a shopping mall and parking lot.

Joey Sorge is a ball of fire as motorcycle-riding Italian-American automobile mechanic Arthur “The Fonz” or “Fonzie” Fonzarelli. But Sorge’s charismatic comic characterization sets the bar so high that few members of the Happy Days supporting cast can jump it. Steven Booth is buoyant but rather bland as high school student and aspiring journalist Richie Cunningham; and Felicia Finley fizzles as Fonzie’s flamboyant former girlfriend Pinky Tuscadero, a touring motorcycle daredevil who still carries a torch for The Fonz.

John Massie and especially Cynthia Ferrer give personable performances as Richie’s parents, hardware-store owner/operator Howard Cunningham and his stay-at-home wife and homemaker Marion, better known as “Mr. and Mrs. C”; Whitney Bashor has little to do but does it well as the Cunninghams’ precocious teenage daughter Joanie; and Chris Fore likewise makes all the right moves in the cameo role of Fonzie’s young cousin and Joanie’s boyfriend-to-be Charles “Chachi” Arcola.

Daniel Robinson and James Michael Lambert hit familiar notes as Richie’s best friend Warren “Potsie” Weber and their friend and class cutup Ralph Malph, respectively; and Molly Alvarez gamely plays the gee-whiz role of Richie’s girlfriend Lori Beth Allen, who’s little more than eye candy here. Barry Pearl makes the most of his brief moments in the spotlight as gritty drive-in owner/cook Arnold Delvecchio, but Matt Merchant and Jeff Sumner (subbing for Matt Walker) are not nearly nasty enough as the insufferable pro wrestlers Myron and Jumpy Malachi — and that absence of nastiness makes their ultimate showdown with Fonzie a snooze.

Director Gordon Greenberg, choreographer Michele Lynch, and music director/keyboard player Bruce Barnes and the Happy Days orchestra strive mightily to inject more oomph into this new musical. But the flimsy plot and the underdeveloped characters sabotage their efforts at every turn. In fact, if you don’t already know who’s who in “Happy Days,” what little humor there is in the dialogue may elude you.

The current Broadway Series South presentation of Happy Days — A New Musical, produced by Robert Boyett Theatricals, in association with McCoy Rigby Entertainment, will complete its Triangle run on Sunday at Raleigh Memorial Auditorium in the Progress Energy Center for the Performing Arts. For ticket prices and remaining show times, see our calendar.