If Giant is the classy, impeccably credentialed new musical of the fall, Scandalous is its disreputable opposite number. This musical aims to tell another big, distinctively American story, the life of evangelist Aimee Semple McPherson, but was conceived and written by Kathy Lee Gifford — a talk show host, for God’s sake. Actually, there’s no reason she can’t put together a musical as well as some of the hacks whose work has made it to Broadway, and she has certainly latched on to a promising subject. McPherson was a pioneer of mass-media preaching on 1920s radio, and she also had a messy personal life that became tabloid fodder when she was accused of faking her own disappearance in order to rendezvous with a lover. But too much of the story is merely narrated rather than dramatized, and we never really get a bead on whether McPherson was a corrupt poseur or a true believer with human flaws. The generic pop-gospel songs by David Pomeranz and David Friedman don’t help much. And though Carolee Carmello, as McPherson, acts her heart out and sings spectacularly, she can’t work miracles.