"Next to Normal" broke new ground in the history of the American musical. With book and lyrics by Brian Yorkey and music by Tom Kitt, it debuted off-Broadway in 2008 and then won the Pulitzer Prize for Drama in 2010. The show now running at Old Academy captures its innovative flair. How many musicals center around the life of a mentally ill character, or have rock music orchestration?

In "Normal," everything swirls around Diana, who suffers from a bipolar condition with unpredictable and violent outbursts that come and go like violent summer storms. Christie Fischer's performance in the lead role makes the production work.

In songs, her pleasing voice and delicate tremolos underscore Diana's labile passion. An expressive stillness alternates with frantic movement. Some of what Diana has to say is unwittingly funny. But you are the one who grasps the comedy because Fischer convinces you that Diana lacks the self-awareness to have a genuine sense of humor.

In his prelude, lyricist Yorkey sums up the play's quest: "Let there be light / Sun and moon a million beams / let it shake me from these dreams / And wake me to what's real / Let us begin to heal / Let there be light."

As a literary metaphor, the contrast of "darkness" and "light" is shopworn and trite. But staging is a different issue. Director Josh Tull with help from set designer T. Mark Cole uses light and darkness to create a dramatic sense of nightmare and shifting reality.

You are often in dim light with only a theater "ghost light" hanging in the rear. Full lights reveal a stage with skewed triangles on the doors and walls papered with cubist imagery. The stage floor is cubist and the central dining table is a surreal mix of white and black stripes that lack a discernible pattern.

The most spooky moments on this stage of darkness and light involve the sudden appearance of teenage son Gabe (Nic Fallacaro). He bursts into family arguments with regular irregularity. Fallacaro has a vaguely ghoulish bearing in his solos "I'm Alive" and "There's a World." Much of the first act is shrouded in the mystery of his presence.

Diana's illness has a dramatic impact on everyone in her family. Tom Stone plays husband Dan. With his no-frills tenor in "I am the one," he laments: "I am the one who cares / I am the one who's always been there / And you just don't know who I am." Dan has no life of his own. He is trapped into being a mere caretaker, the victim of Diana's self-absorption.

Daughter Natalie, played by Casey Bilger, is a teenage girl whose coming-of-age problems are further complicated by her home life. She seeks refuge in Mozart and in a lukewarm relationship with her boyfriend Henry (Sean Tyrik). Though all cast hold their own in solo songs, the family's lack of perfect harmony in "Song of Forgetting" has special meaning and charm.

The musical approach in "Next to Normal" expands the genre. In the Old Academy production, the taped orchestration of music director Cheri Tigh follows Tom Kitt's original rock music format. Speech melds into melodic phrases to match the rise of a character's passion. In post-Sondheim fashion, none of the songs have stand-alone power apart from the dramatic context in which they take shape.

The subject matter is equally modern, shunning the traditional inclination of American musicals toward romance and light entertainment. "Normal" tackles gritty problems, most directly the problem of mental illness and its impact on the lives of others.

The psychiatrist characters are nearly buffoons. In "Who's Crazy/ My Psychopharmacologist and I" Dr. Fine (Ryan Baber) offers a comical pill regimen. When it fails Baber returns to play Dr. Madden in Act 2 who, like a used car salesman, pushes an electroconvulsive therapy cure.

In addition to the deadpan satire of psychiatry, "Next to Normal" puts the self-help canard about "bringing grief to closure" in its crosshairs. It asks, why want to eradicate the memory of our suffering? What would a "cure" feel like? What would the eradication of grief mean?

With its sharp focus on Diana's mental illness, it is easy to overlook the play's larger metaphor. This family is also a typical suburban family, so weak in emotional resources that the psychiatrist becomes a quasi-member. The suggestion of "Almost Normal" is that this modern "nuclear family" is especially vulnerable to the toxic effects of a single member, and easily susceptible to breakdown and dissolution.

Some may find the ending of the play disquieting in its indeterminacy. Diana's solution is like Nora's in Henrik Ibsen's "A Doll's House". The focus of "Next to Normal" is not prescriptive. It falls more on the unhappy nature of the status quo.

Old Academy is located at 3540-44 Indian Queen Lane. "Next to Normal" will run through May 5. Tickets available at 215-843-1109.