A SHOW NEEDS a hook. It doesn't have to grab the audience immediately, but somewhere along the way, a clear idea must take shape. Once an audience becomes hooked, the show can start to move, and the spectators will stay with it until the final curtain, when it releases them. If a show has no clear idea backing it, the cast and crew end up carrying a dead weight. Sometimes a highly talented group of performers and techs manages to breathe life into a show that can't stand on its own feet. More often, as in After Hours, the performance just doesn't "click," and although the singing and dancing entertain, the evening ends up seeming a little pointless.

Billing it as a "Broadway jazz revue," director David McIntosh conceived of After Hours simply as a collection of 19 dance numbers from Broadway musicals of the twenties and thirties. He has made outstanding choices, including hits from the alltime favorite musicals like Kiss Me, Kate and Babes in Arms. McIntosh necessarily draws heavily on the most famous works of Porter, Gershwin and Rodgers, since college students of the eighties are unfamiliar with many great tunes that haven't remained a part of popular culture. The only songs that don't pick up are the slower, less familiar ballads like Porter's "What is This Thing Called Love?" from Wake Up and Dream Unchoreographed, they must rely on the talent of the singer--McIntosh--which, while strong, is not outstanding enough to sustain the show.

During "What is This Thing Called Love?" and David Frutkoff's rendition of Sondheim's more recent "Losing My Mind," After Hours becomes simply a musical recital. Nothing happens onstage, and the tunes lose the original meanings they conveyed as a part of the musicals McIntosh lifts them from. The women's solos work better. Kathy Teague's lively "Thou Swell" and Nancy Cotten's energetic "Nobody Makes a Pass at Me," with typically American lyrics and ideas, capture best the spirit of these musicals.

IN FACT, typical Americana might have provided a successful point of departure for After Hours, better than the barely discernable and categorically almost infinite topic of Love, with which all the numbers have at least a vague connection (but what about "My Favorite Things"?). Perhaps it is even straining a bit to suggest that anything as cohesive as a theme holds this revue together; it seems likely that McIntosh deferred to musical merit in his selections.

Company numbers come off the strongest. The cast of five dance and sing best when all together. Porter's "Too Darn Hot" is the most successful number in the show. The choreography is smooth, the performance fairly polished. The women's trio in "I Can Cook, Too" evoked loud laughter, as did the men's equally amusing rendition of the song in a modern parody of the 1944 Bernstein classic. After Hours could use more of this kind of innovation.

The first act, according to the program, takes place in "A Cabaret After Hours," the second in "A Cabaret." Changes from informal to matching costumes, and from normal to glaring spots in lighting, marked the end of one act and the beginning of the next. In addition, the musicians in the band put away the sixes of Michelob before the second act, or maybe they had just finished them by then. (They managed to keep the beat very well throughout, anyway.) But aside from these contrasts and a long intermission, the "frontstage" and "backstage" of a cabaret don't appear very different.

Almost any attempt at such a "staging" of a revue ends up seeming contrived, despite the best efforts of the director. A revue usually works well only when taken to its logical extreme--when the director and producer put all their efforts into creating a grandiose spectacle. Outrageously elaborate costumes, realistic, intricately constructed sets, a large chorus of Pepsodent smiles, and outstanding singers and dancers can make up for what a revue lacks thematically.

McIntosh's conception of a stark, "theatrical" set, a five-member cast and a three-man band is bound to be difficult to execute. Although the performers are talented and have put a great deal of work into the production, they have set themselves a nearly impossible task. After Hours will entertain you, but you won't get hooked.