That the latter is the full extent of the concept makes Cabaret CooCoo a slender thing—Mark, Sabrina, et al. are applying their virtuosity to a project so light it’s almost airborne. Last year’s Manifesto! demonstrated that Happenstance is best when retrofitting its elegant mummery onto haut concepts—or whittling those concepts down to more clownlike proportions, as the case may be. In comparison, Cabaret comes off a bit like “Her Majesty”after the dizzying suite on the second side of Abbey Road: Charming, but with the whiff of an afterthought.