The same type of amiably flawed characters that inhabit Kenneth Lonergan’s sleeper hit film You Can Count on Me populate his new play, set in the lobby of a Manhattan high-rise. There, an oily veteran cop (Tate Donovan) strands his protegee (Heather Burns) with security guard Jeff (Glenn Fitzgerald) while he visits his mistress. And there, a murder investigation — involving Jeff’s straight-arrow boss (Dion Graham) — casually, inevitably, unravels. Threats are made, loyalties strained, and Jeff (among others) grapples with a miserable choice. The script is deftly shaded: Wisecracks pepper the distress of characters whose motives are realistically impure. It’s capped with a pitch-perfect cast, particularly Fitzgerald’s hapless but well-intentioned hero. Or is that antihero?