The mythology of the guardian angel who descends to earth to save a soul has inspired many a beloved entertainment. Think of It's a Wonderful Life, Carousel or Heaven Can Wait. Now we can add Heaven Help Us!, a clever new musical that stretches credulity even further by asking us to buy Frank Sinatra, Dean Martin and Sammy Davis Jr., as three such angels.

Just go with it.

The result, as evidenced by the talent-packed world premiere at Florida Stage scheduled for the rest of the summer, is a ring-a-ding-ding evening's romp that is both swinging and heartfelt. It still needs some tweaking -- for instance, the story runs out long before the show finishes -- but with more work there is every indication that Heaven Help Us! will be entertaining audiences far beyond South Florida for heaven knows how long.

If the idea seems constructed of borrowed parts -- there are echoes of Forever Plaid, Damn Yankees and Field of Dreams, too -- the writing by Ray Roderick and James Hindman finesses the familiarity. And Roderick's staging is slick enough to disarm even those who were immune to the Rat Pack's charms.

It seems that 25 years ago Sinatra soft-pedaled his opinion of an amateur singer with a seemingly innocent, upbeat white lie. That singer, Vic, the embittered owner of a rundown Las Vegas saloon dedicated to the Pack, is now on the verge of committing suicide for not living up to Ol' Blue Eyes' assessment. So God (as voiced by Gordon McConnell) dispatches the sergeants three to stop Vic from offing himself so they can avoid being kicked out of heaven.

Naturally -- well, as these tales go -- they need to inhabit living bodies. The sight of Davis' manic, slack-jawed gestures coming from the tavern's bald, white bartender (adorable, energetic Eddie Korbich) is alone worth the price of admission. After reconnecting, limbering up with a few signature tunes and running through Shtick styled on the movie All of Me, the trio launches into vocal coaching Vic (a morose, initially pitch-challenged Adam Pelty).

Of course, their song delivery advice is contradictory. Sammy tells him it is about being hip and frenetic, while Dean says the key is being loose and smooth, and to Frank the trick is self-assured phrasing of the lyrics. In one of the show's high points, Vic sings Come Fly With Me using the advice of each Pack member on successive verses.

Heaven Help Us! is so entertaining that even its drawbacks have their assets. The show works so hard not to be a mere tribute concert that it is disheartening to see the story get put on hold in the second act for a recreation of the threesome's Sands Hotel appearances. Still, Korbich sprints through a dead-on handful of celebrity impersonations -- Picture Sammy's version of Katharine Hepburn -- while Julian Rebolledo's alcohol-limbered banter as Dean is strictly 100 proof and Marcus Neville's seemingly effortless, silken ballads all but channel Sinatra and remind us why he was Chairman of the Board among singers.

A show like Heaven Help Us! cries out to have a dame for the Rat Pack to play off, and from her opening number, the luscious Jodi Stevens raises the ambient temperature at Florida Stage several degrees. She plays an assisting angel called Angie, who has a history-changing résumé like Damn Yankees' Lola, but while the part has potential, Roderick and Hindman have not really figured out what to do with her.

Despite these quibbles, this is a much more engaging, theatrical evening than Roderick's I Love A Piano last summer. So loosen your tuxedo tie, sit back, soak up the 30 or so song standards the Rat Pack helped popularize, get an eyeful of Dana Lauren Kenn's memorabilia-strewn saloon set and enjoy five of the most accomplished musical performances ever assembled by Florida Stage.