PITTSFIELD — Wilson Chin's setting for director Julianne Boyd's haunting production of "Sweeney Todd: The Demon Barber of Fleet Street" at Barrington Stage Company, is lean, raw, spare; revealing, even with all its shadowy recesses. It is perfectly emblematic of a production that goes about its business purposefully; with crisp, smooth discipline and focus; which has nothing on its mind but to get out of the way and let a complicated musical about the dark, morally corrupt side of human nature speak for itself.

Set in 19th century London, Stephen Sondheim (music and lyrics) and Hugh Wheeler's (book) "Sweeney Todd" tells the tale of a wrongfully imprisoned barber, Benjamin Barker, who reemerges from jail as Sweeney Todd (Jeff McCarthy). He is seeking revenge against the judge, Turpin (Ed Dixon), who not only sent him to prison on false charges but stripped him of his reason for living -- his wife, whom Todd believes is dead, and his daughter, Johanna, whom Turpin holds as his captive ward and whom he intends to marry.

Todd sets up shop above a meat pie bakery run by Mrs. Lovett (Harriet Harris), who sees in Todd an opportunity to reverse the declining fortunes of her business and her personal life. Recognizing an opportunity when she sees one, the ever-resourceful Lovett capitalizes on Todd's blood lust and persuades him -- in the deliciously witty "A Little Priest" -- to dispatch customers with his razor and serve up the ground remains in her pies.

This is a complicated tale about obsession, moral bankruptcy, the corruption of innocence but Boyd, her uniformly accomplished cast and music director Darren Cohen tell it with a purity and integrity that reaches deep into the story's aching heart.

As Sweeney, McCarthy carefully tracks the arc of a man who, when first we see him, already has been through hell but who still clings to a shred of hope and expectation. The realization that he has lost far more than he thought comes upon him with stunning force. By the time he works his way through the powerful "Epiphany" near the end of the first act, Todd's devastating transformation into hell's agent is complete.

Harris is an absolute revelation, and charmer, as Mrs. Lovett; the perfect complement to McCarthy's brooding, single-minded, mordantly witty Todd. She's a pragmatist who wants nothing more than financial security and, having been a widow for 17 years, a man. She lays out her vision of a perfect life in the nearly showstopping "By the Sea" but as she does there already are signs that this dream, like all the others that have sustained her, will prove to be a fool's vision.

Harris delivers a wonderfully buoyant, full performance that, like everything else about this impressive production, knows its limits without holding back.

"Sweeney Todd" may be built around Sweeney and Mrs. Lovett but Boyd has created a true ensemble here with a cast that uniformly sidesteps the theatrical stylization to which this oh, so brilliant material too often falls prey.

From Ed Dixon's licentious Turpin, Shonn Wiley's decent, upstanding Anthony Hope and Sarah Stevens' touchingly vulnerable Johanna to Christianne Tisdale's unsettling Beggar Woman and particularly Zachary Clause's poignant Tobias, whose protective devotion to Mrs. Lovett proves fateful, there is not a misstep anywhere on stage or, for that matter, in the pit, from which Cohen has Sondheim's score very well in hand.

Even in her least successful productions, Boyd has shown a mastery of stage craftsmanship. But even at her best, there's been something just missing in terms of emotional values. Not here. Nothing is missing here. Boyd's directing has moved to another level. "Sweeney Todd" is her most mature, most fully realized work. What that means for a theatergoer is an evening of theater that is as richly rewarding as you could want.