Flan and Ouisa Kittredge sell art. They believe all their problems will be over if they can clinch a deal on a Cezanne. They find, like many who have been dealing in paintings recently, that their problems are just beginning. This is the plot of John Guare's 1990 play 'Six Degrees of Separation,' the subject of a superb revival at London's Old Vic. Guare paints an icy- affectionate portrait of a middle-class art bubble. It feels contemporary, even 20 years on. The Kittredges's plush life changes when the dashing young Paul is brought into their New York apartment as a victim of mugging. He tells them he's a friend of their children and didn't know where else to turn. Paul is a great cook, an engaging conversationalist, and a beautifully mannered guest. He's also a brilliant con artist. Suddenly the play begins, with exuberant intellectual comedy, to double-deal in the real and the fake. The Kittredges must question the value of everything in their lives, from their rare double-sided Kandinsky to their children's love. At one point Paul delivers a beautiful hymn to the power of the imagination: His self-reinvention from black hustler to suave conman is seen in artistic terms. Later, it's clear that he understands the value of the imagination, not its cost. Value, cost. Cost, value. Guare suggests that there are no easy answers to this riddle, either in art or life. The performances fizz with energy. Anthony Head gives an intriguing edge to the suave Flan Kittredge, and Zoe Boyle and Paul Stocker are amusingly hysterical as his adolescent children. The play's weight comes from the relationship that develops between Ouisa Kittredge (Lesley Manville) and Paul (Obi Abili), who achieve a touching vulnerability. It's funny, it's moving, and ideas fly out like sparks from a whetstone. And all in 90 whirling minutes. A theatrical device that Guare uses cleverly is the direct-to-audience address. So does Douglas Carter Beane in 'The Little Dog Laughed,' with less sophistication. That's not to say that there aren't some whip-smart laughs in his comedy. 'You want my word?' shrieks the bitchy Hollywood agent Diane (Tamsin Greig). 'You're asking a whore for her cherry.' Diane's top client is the young star Mitchell Green (Rupert Friend) who has, as she says, a 'slight recurring case of homosexuality.' When Mitchell gets involved with a bisexual call-boy called Alex, Diane must nip the relationship in the bud to protect his burning-hot image in Hollywood. As a satire, it lacks bite. A leading man can't be 'out' in Hollywood? That's hardly a new plot line. As a comedy, it fares better, especially with Greig's hilarious performance. When Mitchell wonders if he can be an 'out' leading man, Diane shouts incredulously: 'Are you British? Do you have a knighthood? Then no!' Jamie Lloyd's simple production is serviceable, if lacking the elegant tension of 'Six Degrees.' Some scenes meander. The emotions verge on the trivial. There are no ideas about value, cost or imagination sparking off the whetstone here. With Greig's comic bravura, though, it has enough laughs to remain entertaining. _ 'Six Degrees of Separation,' through April 3 at the Old Vic theater; information: www.oldvictheatre.com, 44-844-871-7628. _ 'The Little Dog Laughed,' through April 10 at the Garrick Theatre; www.nimaxtheatres.com, 44-844-579-1974. 