Master Class begins strongly, and abruptly, with the appearance of opera's great diva, Maria Callas (played by Michaela Greeley). There is no transition into theatrical "space" — the lights stay on, the actors come onstage, class begins. Greeley has an immediate presence most actresses should envy. She draws you in even as she pushes you away — the hallmark of a diva's charisma. That's a good thing, because Master Class rests entirely on her. There is no plot to follow: Callas is giving a master class to opera singers, and gets through three of them (in two acts, with two monologues) before it ends. There are no other characters to speak of; yes, there are other actors onstage, and they have names and lines, but they're all foils for Callas. This is a one-woman show with human props. Everything hinges on the diva. Doesn't it always? For the most part, Greeley pulls it off: She's charming, abrasive, insightful, and deep, but wonderfully inconsistent. The only thing she can't do as Callas is be vulnerable (which makes the monologues problematic), but generally she embodies the role in grand style. Like her students, you learn nothing about voice or opera. Divas can never really teach you about their art — their only real subject is themselves. But you certainly pay attention during the lesson.