According to the Heisenberg Uncertainty Principle, it’s impossible to know the location and speed of a moving object at the same time. Accordingly, Heisenberg is an apt title for Simon Stephens’s exciting, bewildering and ultimately exhilarating play, currently presented at the Mark Taper Forum and starring Tony Award-winner Mary-Louise Parker and Tony Award-nominee Denis Arndt. The sole two characters in the play move at such different speeds, live such different existences, that we’re challenged to believe that they can co-exist in the same space. Stephens places tremendous responsibility on the actors to sell this improbable pairing, but fortunately Parker and Arndt, under the acute direction of Mark Brokaw, are up to the task.

Heisenberg opens in a London train station just after Georgie, a 42 year-old American living in London, inexplicably kisses Alex, a 75 year-old Irish butcher on the back of neck. In the course the 70-minute, intermission-less play, Georgie invades Alex’s life, knocking his routine-like existence off-balance. Georgie claims that Alex is the spitting image of her dead husband, but we soon learn that Georgie is a pathological liar and that almost every shifting, changing story she tells is suspect. Did she ever have a husband? Does she have a teenage son living in New Jersey? Is she an assassin? Is she a stalker? What are her motives? Against the onslaught of Georgie’s personality, Alex struggles to maintain his equilibrium, but is no match for Georgie’s “charms.”

Played with breakneck intensity by Parker, Georgie is a fascinating paradox: off-putting, abrasive, annoying, yet hilarious, vulnerable and weirdly ingratiating. Parker handles Georgie’s breathless, stop-and-start, stream-of-consciousness dialog admirably. At times, she slinks about the stage like a tiger, at other times, like a tiger’s prey. It is almost impossible to take your eyes off of her. I only question the decision for Georgie to speak with a strange, almost-drunk slur that’s never explained. In the hands of Parker, Georgie doesn’t need affectations to be annoying – or endearing.

Though Georgie is the showier of the roles, both roles are equally complex. Arndt received a Tony nomination for his portrayal, and it’s easy to see why. His performance is a slow-burn, full of nuance. At first, Alex seems reserved, logical and unemotional. He’s a blank slate for the audience, reacting as we would to Georgie’s offbeat ramblings and the bizarreness of the situation. But slowly, Arndt reveals Alex’s layers, his losses, and his sexual reawakening, becoming more than a foil to Georgie – becoming a true partner in this two-hander.

Mark Wendland’s sets are spare, consisting of a couple chairs and tables that are moved about by the actors to simulate different locations. Mark Brokaw’s direction, like Stephens’s dialog, places the emphasis on the actors and their ability to create relationships in the midst of uncertainty.  Heisenberg comes to the Mark Taper from the Manhattan Theatre Club after successful off-Broadway and Broadway runs. Parker and Arndt reprise the roles they created off-Broadway and on Broadway.

— Chiedu Egbuniwe

Heisenberg runs at the Mark Taper Forum through August 6th. The running time is 70 minutes, no intermission. Tickets start at $25 and can be purchased at www.centertheatregroup.org.