Envy gets a bad rap. Yes, she’s one of the Seven Deadlies, and yeah, she’s got a couple Commandments all to herself. But what your Sunday school teacher never told you about Envy is that, under the right conditions, she can be a powerful muse. Green-eyed case in point: The Four of Us, Itamar Moses’ witty, engaging (if slightly overlong) two-character play about the 10-year friendship between a young novelist and a young playwright. Karl Miller is the sardonic, self-doubting playwright who struggles with the sudden and outrageously lucrative success of his friend’s first novel. Happily, it’s a hell of a lot of fun to watch an actor as naturalistic and unself-conscious as Miller do the requisite struggling: He pads around the stage in a sleepy, discomfited daze; we sense that he’s sincerely happy for his friend even as jealousy roils in his gut, causing him to bite the ends off his sentences. Moses isn’t saying how much he based The Four of Us on his own friendship with novelist Jonathan Safran Foer (though “a whole lot” is reportedly a safe bet.) But even leaving the specific meta-considerations aside, the fact remains that writing about writing can’t help but put audiences on high alert for self-indulgence and insularity. Moses and director Daniel De Raey are determined to avoid such pitfalls by presenting a rigorously evenhanded account of the friendship—no stacking the deck in favor of Miller’s lean-and-hungry playwright. That’s a laudable goal, and it bespeaks the production’s commitment to avoiding easy answers and tidy lessons. But if anything, they succeed too well: Dan Crane’s novelist is so guileless and self-possessed that the conflict between the men can feel dramatically diffuse, especially around the play’s midpoint, when De Raey lets the pace slacken during an aimless, pot-fueled discussion that’s long on stoner verisimilitude but short on narrative moment. Moses’ layered, chronologically fragmented script, and the performers’ crisp comic timing, more or less make up for this energy deficit, though, and there’s always designer Tony Cisek’s backlit, Mondrian-inspired wall panels to marvel at, whenever the dialogue takes an inward, lonely-is-the-road-of-the-artist turn. When the night is over, you may find yourself wondering if that final scene did all the work Moses asked of it. You may also come away convinced, as I did, that inside the very good 2-hour play you just saw lies a truly great 90-minute play.