With “Darling Grenadine,” composer-lyricist Daniel Zaitchik emerges as a songwriter not only to watch but to enjoy at this very early moment in his career. Two years ago, he won the Kleban Prize for most promising musical theater lyricist, and with this new musical, it’s clear that his music is every bit as wonderful as his sophisticated word play.

That latter literary talent somehow does not extend to his coining a great title for this show: “Darling Grenadine,” which opened Monday at Roundabout’s Off-Off-Broadway space, the Black Box Theatre. But there hasn’t been a new score this unabashedly romantic and soaring since Adam Guettel gave us “The Light in the Piazza,” which hit Broadway back in 2005.

The Roundabout’s Black Box houses well under a 100 seats in its current configuration, with Zaitchik’s musical being performed in the round. The cast of six doesn’t have more than a bed, a bench and a liquor bar to support them. Nevertheless, Michael Berresse’s fluid and low-key direction creates a vivid sense of time and place by surrounding the audience with screens (set design by Tim Mackabee) that drop us into a black-and-white Manhattan fantasy world (projection designs by Edward T. Morris). It all makes for a most unusual in-the-round experience.

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Zaitchik also writes the book here, and typically that triple threat is not a good sign. It’s nice that he provides us with an original story, and not one based on a famous movie. The score is so attractive from the get-go that the very ordinary romance of Harry (Adam Kantor) and Louise (Emily Walton) engages even as you wish something highly unusual would happen between them. She’s a featured actor in a Broadway musical titled “Paradise” and he’s a songwriter of TV commercials who has enough money to invest in his step-brother’s bar, where he sometimes performs standards at the piano. At Louise’s insistence, Harry finally consents to perform an original song, “Manhattan,” and she’s duly impressed by his talent.

It says much about Kaitchik’s talent that “Manhattan” and the show’s two other stunning melodies, “Suspended” and “Paradise,” are not woven into the story. “Manhattan” is essentially an audition, and the other two songs are from the musical “Paradise” within the musical that is “Darling Grenadine.” Maybe Zaitchik the songwriter needs to be freed from Zaitchik the book writer? This barroom-sink story doesn’t always give full expression to what are very operatic aspirations.

The simple story told here does have its charms and, ultimately, its dark secrets. I prefer it to the complicated narrative mess that is “Moulin Rouge!” or “Jagged Little Pill” or “Girl From the North Country,” three musicals that tell too much story as if to make up for their lack of original scores.

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Eventually, something significant does take place between Harry and Louise. And Kantor is so charmingly headstrong in his pursuit of love that, like his new girlfriend, you might find yourself making excuses for him.

It’s possible that Zaitchik judges Harry more harshly than the character deserves. The book would be stronger if Harry’s enabling step-brother (Jay Armstrong Johnson) shared some of the guilt. Despite Walton’s winning performance and gorgeous vocals, Louise remains a cipher, and her “All About Eve” moment doesn’t resonate.

More successful is the depiction of Harry’s attachment to his dog, Paul. It’s very of-the-moment that many citizens of this city think of their pets as people. Totally enchanting is the way in which the Trumpet Player (Mike Nappi) evokes Paul while also providing musical segues between scenes.

Now, about that title, “Darling Grenadine.” Lose it.