How does brilliance respond to mediocrity? It’s one of the dynamics at work in Moisés Kaufman’s “33 Variations’’ — and it’s a question that Paula Plum implicitly answers with a performance at Lyric Stage Company that manages to transcend the limitations of an ambitious but deeply flawed and erratic play.

Plum’s artistry is not exactly news to Boston theatergoers. But we shouldn’t take for granted her extraordinary range, or the depth, wit, and fierce intelligence she brings to role after role. In “33 Variations,’’ directed by Spiro Veloudos, she delivers a subtly modulated, consistently engrossing portrayal of a not-terribly-likable protagonist, earning sympathy for a character who would never ask for it. Plum has made a career out of that kind of skillful balancing act.