NEW YORK - In the orchestra pit, the conductor wears a formal, 18th-century wig. On a stage crowned by a church organ and sprouting floor-to-ceiling girders at all angles, 20 performers are gargoyles, boys and girls, adults, ghosts. Twenty more, a choir, punctuate the story from a balcony that sweeps across the upper stage. Seven chamber musicians play far below them.

Coram Boy, the National Theatre of Great Britain's production that opened last night with an American cast, is epic in every gripping sense. Its intricate plot covers nine years in an age of British enlightenment both spiritually exhilarating and staggeringly cruel. The play is a triumph of stagecraft, directed by Melly Still and magically lit by Ed McCarthy; their attention to theatrical detail convinces you that choking a toy doll is real infanticide and that people can free-fall into the sea without so much as a drop of water present.

Coram Boy is an intersection of stories about a criminal whose greed overwhelms anything human inside him, the moneyed denizens of a wealthy country estate, and a unique (and real) London orphanage in a country strewn with street foundlings barely past their toddler years.

Like epics in general, Coram Boy has its stretches. It asks us to believe, at one point, that a doomed prisoner could be saved by the stealthy intervention of a housemaid. And its resolution - tremendously satisfying to an audience on the edge of its collective seat - seemed unlikely to me once I had left the inspired cocoon in the Imperial Theatre for the hard-boiled New York subway tunnels. As I write this, the next morning, the ending in fact seems downright laughable.

But during the entire preview performance of Coram Boy, I bought it and - like the people around me, I sensed - was engulfed by Helen Edmundson's adaptation of Jamila Gavin's prizewinning young-adult novel. It is acted with no celebrities and no real casting hierarchy; at the curtain call, you see one huge family of players.

The show is by no means an opera, but it unleashes a staggering operatic power. It's not a musical but employs music as if it were; it even includes a piece of Handel's Messiah, and everyone in the cast has the pipes to bring it off. Women play grade-school boys and sing uneasily, just like them; in two cases when their characters reach puberty, men seamlessly assume the roles. Hats off to Xanthe Elbrick and Charlotte Parry and their successors in the parts, Wayne Wilcox and Dashiell Eaves.

Others are equally impressive: Uzo Aduba as a black waif; the dexterous Brad Fleischer as an abused, addled boy; Ivy Vahanian as a love interest; Christina Rouner as a well-heeled woman with a heel of a husband; and Bill Camp and Jan Maxwell as the villain and his not-always-willing accomplice.

Coram Boy is a methodically planned trip into another world - at times funny, sad and even wrenching. It has a genuine feel, bred from inventive people who understand the power of live performance. You may know your way around, but you'll lose yourself in its thrall.

Coram Boy

Adapted by Helen Edmundson from the novel by Jamila Gavin. Directed by Melly Still, set and costumes by Still and Ti Green, lighting by Ed McCarthy, sound by Christopher Shutt, music by Adrian Sutton, music direction by Constantine Kitsopoulos, fight direction by Thomas Schall. Presented by the National Theatre of Great Britain.

The cast: Brad Fleischer (Meshak), Xanthe Elbrick (young Alexander), Wayne Wilcox (adult Alexander), Charlotte Parry (young Thomas), Dashiell Eaves (adult Thomas), Uzo Aduba (Toby), Bill Camp (Otis), Jan Maxwell (Mrs. Lynch), Ivy Vahanian (Melissa), Christina Rouner (Lady Ashbrook), David Andrew MacDonald (Lord Ashbrook), Kathleen McNenny (Mrs. Milcote).

Playing at: Imperial Theatre, 249 W. 49th St., New York. Tickets: $56.25 to $101.25. Information: 1-800-432-7250 or www.coramboyonbroadway.com.

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Contact staff writer Howard Shapiro at 215-854-5727 or hshapiro@phillynews.com. Read his recent work at http://go.philly.com/howardshapiro.