Laura Dreyfuss and Ben Platt in “Dear Evan Hansen” at Arena Stage. ( Margot Schulman)

If your upcoming vacation plans allow you any flexibility, then by any means possible add “Dear Evan Hansen” to your itinerary. The heart-piercingly lovely new musical, receiving its world premiere at Arena Stage, is a trip to the exciting place that musical theater sometimes takes you, a destination of wholly unexpected impact, where characters burst into song and you, in spite of yourself, into tears.

No mere midsummer romp, the musical, with a top-flight contemporary pop score by Benj Pasek and Justin Paul and an equally accomplished script by Steven Levenson, is as serious-minded as it is playful. Directed with exceptional intelligence by Michael Greif, the show is on one level a sly romantic comedy, the story of a high school caper gone risibly awry. On another, it’s a cautionary tale for our times, about the double-edged seductiveness of finding “community” on the Web. On still another, it’s a nuanced account of lying and being lied to — and how there can be surprising advantages on both the giving and the receiving end of a deception.

It features, too, a most extraordinary performance by Ben Platt as the Evan of the title, a withdrawn teenager of desperate neediness whose elaborate charade gives solace for a time to a grieving family of which he longs to be a part. Platt’s ability to elbow complicated Evan so effortlessly into our affections attests to an achievement bordering on heroic. The splendid acting extends to all seven of his cast mates, and especially to Rachel Bay Jones as his stressed single mom and Laura Dreyfuss, playing the girl with whom nerdy Evan falls in love.

The production in Arena’s Kreeger Theater, on David Korins’s sleekly becoming set, reveals to audiences a musical-writing team that successfully scales a new plateau; Pasek and Paul showed a lot of promise in their 2012 off-Broadway musical adaptation of the indie movie “Dogfight”; “Dear Evan Hansen” — on which playwright Levenson now joins them — is a whole other magnitude of accomplishment.

It’s an entertainingly smart piece, with several lilting ballads that you’ll immediately want channeled into your ear buds, including “Only Us,” a buoyantly melodic duet for Platt and Dreyfuss; Platt bears the bulk of the vocal load in the show, and his highly charged renditions of songs such as the operatically anguished “Words Fail” illuminate the astonishingly wrenching route that Platt is willing to explore here. Evan feels like a freshly minted variety of hero for musical comedy, and Platt finds an endearing physicality to help us see him as such, in a shyness and awkwardness so painful he blinks nervously and talks to other people with his eyes trained firmly on his feet.

Ben Platt, left, as the title character, with the grieving parents (Michael Park and Jennifer Laura Thompson) of “Dear Evan Hansen.” ( Margot Schulman)

Because Evan is the single-minded fixation of “Dear Evan Hansen,” our understanding of his actions at every step of the 2 1/2 -hour show becomes an absolute imperative. And although we’re clear on his motives and decision-making much of the time, there’s a crucial transition in Act 2 when the show’s creators let us down just a bit. What’s not worked out adequately at present is why, after Evan gains so much from the ruse he’s painstakingly constructed, he makes a choice that will change the outcome of the entire story.

It’s not so much a problem with the choice itself — which feels right — but with enlightening us on how he’s come to it. Any hint of what he’s thinking about this choice, or who, even unintentionally, might have put the idea in his head, is confoundingly missing. So the pivot feels too abrupt. (For fear of giving away too much, I have to remain a tad vague on this point.) The result, however, is that the show’s final 15 minutes, while still very moving, aren’t developed to their full consoling potential.

This is important because “Dear Evan Hansen” otherwise radiates so much confidence and humor and insight about Evan and the people in his orbit. Cleverly, the show uses the tools of modern interaction — a therapist’s dictates, the behavioral codes of social media — to aid Evan in his scheme, to trick the world into believing he was friends with someone he hardly knew. It’s triggered by a series of seemingly random minor events: the writing of one of Evan’s affirmation letters to himself, an exercise suggested by his therapist (and which gives the show its title); the signing of the cast on his arm by another high school senior; and his encounter with that student’s stricken parents (the sterling Jennifer Laura Thompson and Michael Park) after they’ve learned of his sudden death.

An innocent misunderstanding about Evan’s relationship to their troubled son Connor (Mike Faist, another terrific turn) gives Evan the opening to be the person worthy of the attention he desires. As in all good farce, the complications pile on, as a computer-savvy classmate (the enjoyably caustic Will Roland) agrees to help Evan in his deception and a fellow nerd (the fine Alexis Molnar) becomes his unwitting partner in mythologizing Connor’s life and Evan’s place in it. The consequences of the escalating mendacity are nowhere more profound than in Evan’s relationship to Connor’s skeptical younger sister, Zoe, in whom Dreyfuss invests an irresistible mixture of tenderness and adolescent discontent.

Greif, a director who’s shown a deft hand with sophisticated musicals, such as the Pulitzer Prize-winning “Next to Normal,” provides a superbly balanced platform here, allowing the actors in both the dialogue and musical scenes to “sing” with touching authority. (Jones is particularly effective, in integrating speeches and songs into her evocation of a fatigued mom’s loving exasperation.) With the help of some excellent musicians and designers — music director Ben Cohn, orchestrator Alex Lacamoire, sound designer Clive Goodwin and a seven-member band — the show’s melodic emotionality gets solid support. And Peter Nigrini’s projections, accompanied by 16 recorded voices, turn the Web itself into the show’s virtual ninth character.

It is Platt’s Evan, though, who is the first among equals in this transfixing endeavor. His performance is proof positive of how much wonderful truth can emerge from the most scandalous of lies.

Dear Evan Hansen

Music and lyrics by Benj Pasek and Justin Paul, book by Steven Levenson. Directed by Michael Greif. Set, David Korins; costumes, Emily Rebholz; lighting, Japhy Weideman; orchestrations, Alex Lacamoire; music director, Ben Cohn; sound, Clive Goodwin; projections, Peter Nigrini; choreographer, Danny Mefford. With Mike Faist, Alexis Molnar, Will Roland. Through Aug. 23 at Arena Stage, 1101 Sixth St. SW. $40-$70. Visit arenastage.org or call 202-488-3300. About 2 1/2 hours.

"Dear Evan Hansen" with Ben Platt is now playing at Arena Stage. Directed by Michael Greif with music and lyrics by Benj Pasek and Justin Paul. (Courtesy Arena Stage)