Xanadu

Fun summertime fluff, or the end of musical theater as we know it? It all depends on how you view the cinematic source of Xanadu, the stupefying 1980 Olivia Newton-John vehicle/camp touchstone. The story is barely intelligible — a muse (Kerry Butler) descends from Mount Olympus to inspire a suicidal pavement artist (Cheyenne Jackson) to open a roller disco; the songs, save guilty pleasures like ''Magic'' and ''Evil Woman,'' consist of enough disco-lite B sides to fill a PBS pledge-week special. Note to anyone eyeing the rights to Can't Stop the Music: We will hunt you down. C