Prolific playwright Steven Dietz (God's Country, Lonely Planet) has set himself a challenge: write a spy/conspiracy thriller for the stage, set in a dusty Manhattan bar, where the action has to live in the language, not in car chases or James Bond parkour. He succeeds. Yankee Tavern goes from goofy—the evil hermeneutics of Starbucks—to chilling, real-life oddities about 9/11 that are difficult to explain away. There's a steely stranger who always orders two Rolling Rocks but only drinks one, an exasperated and naive bar owner, and a deeply entertaining performance by Charles Leggett as Ray, a blustery, cranky conspiracy theorist who might be closer to the truth than anybody gives him credit for. (ACT Theatre, 700 Union St, 292-7676, $10–$50, 2 and 8 pm)