A quarter century ago, Mary-Louise Parker played a gorgeous, seemingly ditsy bride whose life changed after she was kissed by a very old stranger in Craig Lucas' "Prelude to a Kiss." Parker again plays a gorgeous, possibly flaky woman in Simon Stephens' "Heisenberg," but, this time, she's the one who changes lives (hers and someone else's) when she impulsively kisses the back of an older man's neck at a London train station.

Where the earlier play dealt with genuine magic, Simon's unlikely two-character love story creates emotional enchantment through fine-tuned, closely observed character studies. Presented on a small runway dividing Manhattan Theatre Club's tiny Stage II, Parker and the equally impressive Denis Arndt peel layers away from these mismatched, lonely grown-ups, who are as confused and fascinated by their history and future as we are.

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Mark Brokaw directs the intimate 80 minutes, which explores the relationship, with just two chairs, two tables and an ever-changing search for soft spots in the boulders that people build around themselves. Arndt plays a self-contained butcher from Ireland who cries at unexpected events. Parker plays a teacher's aide who lies about herself. She has an aggressive, almost feral physicality. She may be a stalker, a scammer, or just the kind of babbler who gets magnetized by the vacuum created by quiet, shy people.

The title, a curveball, refers to the German physicist's uncertainty principle about the limits we can know about variables. But we can be certain, I think, that this hot-ticket can play as long as its actors feel like it.


WHERE Manhattan Theatre Club Stage II, 131 W. 55th St.

INFO $75; 212-581-1212; manhattantheatreclub.com