Not such an opportunistic guy, that Harold, as played by Alec Baldwin in “Orphans.” Kidnapped at knifepoint by a predatory “dead end kid” in North Philadelphia, the urbane gangster awakens one morning tied to a chair and guarded, if you can call it that, by his abductor’s younger brother, the simple-minded and impressionable Phillip.

Any criminal mastermind worth his fedora would choose this moment to escape, and Harold easily manages his way out of the ropes. But instead of high-tailing it out the door, he sticks around, and by the second act of the dark fable, which has just opened at the Gerald Schoenfeld Theatre, Harold is no longer a prisoner; he’s a de facto parent. Which is good, because the two kids at the center of Lyle Kessler’s brutal play sure need one.

Treat (Ben Foster, of the upcoming “Kill Your Darlings”) and Phillip (Tom Sturridge, “Being Julia”) have been living for years in a dilapidated row house in North Philadelphia. Treat, a street-smart thug, has been supporting his damaged younger sibling by petty thievery, proud of his ability to put mayonnaise on the table. Treat has abducted Harold, himself an orphan, with the idea that the man’s riches will keep the brothers in StarKist for the rest of their days. As the story unfolds, though, it’s apparent Harold, with his briefcase full of stocks certificates, masterminded his own abduction.

It’s impossible to contemplate how long Treat and Phillip have been on their own, or even, at first, why Harold stays. We’re not meant to overthink such matters: Kessler’s play, first produced 30 years ago, is considered to be in line with the literature of magical realism. Other mysteries here involve the origins of a red high-heeled shoe and a mystical representation of Errol Flynn, who can be seen only by Phillip. This production was directed by Daniel Sullivan, who most recently helmed the “Glengarry Glen Ross” revival at the same theater.

Baldwin’s Harold, in his puffy and pompous glory, is here to redeem the boys, and he does so with cold cash and fatherly advice. He hires Treat as his bodyguard (why would Harold need one of those?), dressing him in the finest suits, while helping Phillip, who has never left home (quite literally, thanks to a long-ago allergy fright) get a sense of his place in the universe via that pre-smartphone tool we all once used to get around: a paper map.

The comic timing we’ve come to associate with the Tony-nominated Baldwin (1992’s “Streetcar” revival) is on grand display, from the moment he escapes his captor’s knots (“Yiddisha boy, Houdini. Don’t let the Italian flavor fool you,” he deadpans, as an awed Philip watches on) to a scene toward the play’s climax, where he guides the boys through a hypothetical scenario about a battle for personal space on a city bus.

Foster’s shady Treat vacillates between menacing and childlike; at any point, you fear he may knife Harold, or hug him. Treat’s own self-worth has come over the years from knowing he is Phillip’s protector. As Harold opens up Phillip’s world, Treat becomes more volatile, flying into a full-on rage when he discovers that Phillip has been hiding a stash of books under the sofa cushions. Turns out the supposedly dim Phillip has even underlined the potent passages. (Treat was to have been played by “Transformers” star Shia LaBeouf, who left the cast after a dust-up with Baldwin, tweeting the drama on his way out the door.)

Sturridge is phenomenal as Phillip, the type of fellow we’d think of today as falling somewhere on the autistic spectrum, though such classifications likely weren’t part of Kessler’s vernacular back in the day. His Phillip inhabits the tiny confines of the row house like a cat, leaping lithely from sofa to stairs to windowsill (the appropriately glum set is by John Lee Beatty).

Though Phillip knows the name of every brand name prize given away on “The Price Is Right,” his confidence and independence are stymied by the sheltered existence Treat has forced on him. All three men have obvious weaknesses, but Phillip is the only one so fragile we fear for his well-being.

Though this marks the first Broadway staging of “Orphans,” the play has had a vibrant life since its 1983 Los Angeles premiere, which featured a young Joey Pantoliano as sweet Phillip. After a 1985 production at Chicago’s Steppenwolf Theatre, it had a well-reviewed Off-Broadway run in New York and was subsequently produced in London, with Albert Finney as Harold. A film followed. Baldwin became interested in the property after he saw Al Pacino do a reading in 2005.

As “Orphans” heads toward its conclusion, it veers from dark comedy toward tragedy. Harold commits a heroic act that transforms him from a one-dimensional Godfather-like figure into someone we worry for. Boiled down, “Orphans” is a dark comedy about the elemental need for companionship. The message is: We all need someone to look after us ... even if it doesn’t always improve our lot.

“Orphans,” at the Gerald Schoenfeld Theatre, 236 W. 45th St., through June 30. Tickets: $67-$132. Call 212-239-6200, or visit Telecharge.com.

Follow Robert Kahn on Twitter@RobertKahn