To call the expansive repertoire of Stephen Sondheim impressive would be the understatement of the year. A legend in the theater world, he has proven himself a master of psychological musical theater time and time again with works as diverse as “Sweeney Todd” and “Into the Woods.”  However, his little-performed play “Passion” arguably surpasses them all, running the gamut of human emotions in just 90 minutes.

The Classic Stage Company’s intimate production more than does justice to the dark and emotional piece. A meditation on the meaning of love, which expertly avoids the melodrama this premise suggests, “Passion” tells the story of Fosca (Judy Kuhn), the unlovely invalid living at a military outpost where her cousin is the colonel. The handsome Giorgio (Ryan Silverman) is transferred there from Milan, where he leaves behind a lover with a beautiful face and a husband. The small kindness he shows Fosca upon his arrival quickly propels her into obsession, which leads to his repulsion, and a destructive dance begins for both of them.

Fosca comes through most powerfully in Sondheim’s lyrics. One of the most poignant moments in the show comes during the song “I Wish I Could Forget You,” as Kuhn leans forward earnestly in her chair to insist, “That doesn’t mean I love you.”

The desperation of the music is brilliantly punctuated with James Lapine’s quick-witted dialogue. Normally, recognizing the quality of the book in a musical could mean pointing out a shortcoming in the songs, but in this case, it is a testament to the skill of Lapine, a longtime Sondheim collaborator (“Into the Woods,” “Sunday in the Park with George”).

John Doyle directs with a shrewd and delicate touch in this bare-bones production, leaving the space to be filled with the actors’ monumental performances. Kuhn, best known for her Tony-nominated turn as the original Broadway Cosette in “Les Misérables” comes into her own with this tragic role. She embodies Fosca wholly and passionately.

Silverman rises to the challenge with formidability, embracing every flaw and complication of Giorgio without apology. Together, the pair provides one of the standout performances of the season.

“Passion” is playing now through April 14 at the Classic Stage Company, located at 136 E. 13th St.

A version of this article was published in the Wednesday, March 13 print edition. Olivia George is theater and books editor. Email her at [email protected].