The junk dealer is just the most obvious bit of terrific in Joy Zinoman’s swan-song production at the Studio Theatre, but boy, is he ever terrific: Grubbily paternal, weary and watchful, dangerous and mean but wholly human, Ed Gero’s Donny Dubrow will break your heart, if he doesn’t break your head first. A biggish dog among small-time hoods in a marginal ’70s Chicago neighborhood, Donny has earned the respect of swaggering, blustery Teach (Peter Allas) and vague, strung-out Bobby (Jimmy Davis) in part because he’s the cunning, level-headed, methodical one in the bunch—though that’s relative at best, as will become clear when the half-baked heist at the story’s center begins to unravel. Donny, having sold a rare buffalo nickel to a collector for what he suspects is too little, means to steal it back, and the rest of the man’s coins along with it. Sniffing a big haul, and arguing that unreliable Bobby won’t make the best assistant, Teach talks his way into being second-story man on the job. The rest of the play’s brisk two acts is mostly about ratcheting up the tension as the older guys wait for another conspirator who never arrives, wondering the while whether Bobby has betrayed them, whether out of anger or the need to feed a jones. Allas’s Teach has the quick temper of a man who senses he’s not quite as smart as he needs to be in a culture where savvy can mean the difference between success and scraping by; Jimmy Davis’ Bobby is twitchy and vulnerable, but alert sometimes too, just alert enough to make you wonder if there isn’t something behind Teach’s suspicions. Zinoman’s pitch-perfect production, caged in Russell Metheny’s fantastically grimy junk-shop set, leaves you feeling like an invisible fourth member of this hapless hardscrabble dog-pack, watching the others circle and sniff and snarl, knowing the first lunge and the first bite are coming any second. It’s gruesome and profane, raucously funny and wrenchingly sad, and it’s one of the finest acts of theater you’re likely to see this year.