What's going on inside Hench's head? There's no way to be sure, but boy, do you ever want to find out. As played by the outstanding Lucas Hedges, the 16-year-old boy-man-boy at the center of Anna Jordan's play Yen, which just opened at the Lucille Lortel Theatre in an MCC Theater production, is clearly in the grip of feelings and thoughts he can't express—and, most likely, doesn't even comprehend. He knows that his current existence is untenable, that he has no real connection to his family, and that he needs something more to be complete, but that's not enough to drive him from the inexorable course of pain, rage, and loss he's been on for his whole life. And for that, if nothing else in Trip Cullman's grating production, you'll be infinitely grateful. . . .