NEW YORK – Hey, old friend.

More than 40 years after notoriously flopping on Broadway, “Merrily We Roll Along” is back with a splendid and shattering revival at the Hudson Theatre starring Jonathan Groff, Lindsay Mendez and Daniel Radcliffe.

Originally directed by Hal Prince, with a marvelous score by Stephen Sondheim, the decades-spanning musical follows the rupture of a friendship but told in reverse. The story begins in 1976 with the bitter falling-out between three middle-aged chums and eventually ends in 1957 with their starry-eyed first meeting in college.

The show's 1981 production featured a mostly teenage cast and was roundly rejected by critics for its muddled design and backward structure. Audiences were similarly unmoved, and the musical shuttered just 16 performances after opening night.

Now brilliantly reimagined by director Maria Friedman, this crushing new “Merrily” evokes the spirit of a haunted house, as jaded movie producer Frank Shepard (Groff) wanders through his stark Los Angeles abode, reflecting on the dreams and companions he left behind in New York. Those include Charley Kringas (Radcliffe), his modest former songwriting partner; Mary Flynn (Mendez), a theater critic with an unrequited crush on Frank; and Beth Spencer (Katie Rose Clarke), his ex-wife and an aspiring singer.

Some of Friedman’s most obvious fixes are cosmetic. The original production was made to resemble a high school gymnasium, and actors wore plain T-shirts with their characters’ names splashed across their chests. Here, there’s no confusion about when and where the story takes place, thanks to Soutra Gilmour’s swank period sets and effortlessly chic costumes. The revival cast is also age-appropriate, allowing them to more effectively run the gamut from youthful optimism to the wistfulness and cynicism of adulthood.

But some of the most vital shifts are in the story itself. The show’s central conflict revolves around Frank and Charley, who co-wrote the songs for a wildly successful yet frivolous Broadway musical. Charley wants to leverage their newfound fortune to finally get their longtime passion project off the ground, while Frank is content to follow the dollar signs to Hollywood and beyond.

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While past “Merrily” productions may have painted Frank as a mere sellout, Friedman recognizes that it isn’t so black and white. Here, we more clearly understand the financial burden of Frank’s messy divorce, and that the romanticized life of a struggling artist is no longer prudent with a young son at home. Self-serving or not, he also enjoys the fabulous parties and pals that come with fame, including his leading lady-turned-mistress Gussie Carnegie (a scene-stealing Krystal Joy Brown).

“Why is it old friends don’t want old friends to change?” Frank sings in the perceptive “Growing Up,” suggesting that he hasn’t abandoned his dreams but simply “readjusted” them.

Groff, who last appeared on Broadway in the original cast of “Hamilton,” has never been better than he is here, imbuing a tricky character with tearful sincerity and charm. Mendez is a hilarious knockout as the acerbic Mary, bringing powerhouse vocals and aching vulnerability to showstoppers “Now You Know” and “Not a Day Goes By.”

As Charley, Radcliffe is the tender, open heart of “Merrily.” The sprightly “Harry Potter” star, now in his fifth Broadway outing, infuses his stubborn lyricist with brio and palpable hurt. He deftly zips through the spiky tongue-twister that is “Franklin Shepard, Inc.,” and his gentle rendition of the show’s signature tune, “Good Thing Going,” is a quiet stunner.

“Merrily” is the latest in a flood of Sondheim revivals, following the legendary composer’s death in 2021 at 91. Since then, “Company,” “Into the Woods,” “Assassins” and “Sweeney Todd” have all graced New York stages to varying degrees of success, while an unfinished Sondheim musical, “Here We Are,” is playing a limited run off-Broadway.

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But “Merrily” is the most top-to-bottom perfect production of them all, from its muscular orchestrations to its vibrant ensemble to its sneakily devastating book by the late George Furth. Part of what makes the show so overwhelmingly emotional is that it transports us back to a more idealistic age: when possibilities seemed endless, friends were forever, and hopes weren’t yet dashed by life’s realities.

"It's our time, breathe it in," Frank sings at the end of the show, as he readies to take on the world with Charley and Mary by his side. The same could be said of "Merrily," which four decades later, finally feels right on time.