In a posh Manhattan condo, a glamorous couple looks back on what went wrong, to taunt, tease and maybe gloat a little. Their young guests are more starry-eyed but still wary, even as they begin to fall in love. Nearby, an astute observer adds his insightful songs to the mix. And what songs! They're all Sondheim, which means all elegant and smart and drop-dead droll.