Torrents of lyricism and floods of Gaelic quaintness pretty much swamp "An Island of No Land at All," Peter Coy's ambitious, atmospheric but unfocused new play being premiered by the Keegan Theatre.

Based on the work of Irish American author Donn Byrne (1889-1929), "Island" relates a heart-wrenching love story -- the star-crossed relationship between a sailor and a mysterious, neurotic nun in Ireland and other parts of Europe in the late 19th century. But Coy's script lingers so long on novelistic detail and evocations of setting -- passages that feel pasted in from Byrne's fiction -- that the central romance never achieves the prominence and clarity it deserves.

Only after a good half-hour of flashing between times and characters, for example, does the play really zoom in on its fascinating heroine: Joan Bruce-Bennett, a charming, fragile nun who has a bad habit of babbling nursery rhymes when she gets nervous. When Joan falls for deBourke O'Malley, an earnest young sailor who has returned to his family's estate outside Dublin, the upshot is tragedy. Fleeing scandal and wrestling with spiritual crises, the lovers roam uneasily around Europe, allowing the play frequent excuses for conjuring up picturesque locales: the bridges of Paris, the blue sea off Monte Carlo, the palm trees in the sultry South of France.

But since "Island's" infatuation with the Emerald Isle rivals O'Malley's love for Joan, the script keeps doubling back to Ireland and the Irish. Ah, the sprigs of white heather that bloom in the glen and bring luck like the four-leaf shamrock! And the Children of Lir who turned into swans as they swam on the mystical waters of the Moyle! The Hibernian flavorings are undeniably piquant and poetic, but they only exacerbate the script's diffusion.

Director Mark A. Rhea does a valiant job of keeping the work's sprawling tendencies in check, moving the nine actors fluidly around a barroom: candlestick- and-bottle-cluttered shelves fronted by a counter where a few actors loiter throughout both acts, playing cards and miming conversation, as if at an Irish pub. Anchoring Stefan M. Gibson's set, with steps representing the Irish countryside going behind and above it, the barroom tableau lends the staging an intimacy, and it bolsters the story's religious and sociological motifs. After all, it's partly the knowledge of the unforgiving judgments people might reach while swigging a beer that heightens Joan's distress and sets her to rattling off bits of nonsense verse.

In the role of Joan, Ghillian Porter exudes a brittle blitheness that makes the tale's denouement all the more poignant. Playing O'Malley, Eric Lucas cultivates the kind of laid-back, matinee-idol panache one might expect from an actor who, according to the program notes, was Brad Pitt's stand-in during the filming of "Twelve Monkeys" (Lucas is, additionally, the author of "Tattoo Sky," also receiving its world premiere at the Keegan this summer). But it's Brian Hemmingsen, as the brooding Mr. Moore, who has the most stage presence, ranting or rhapsodizing in a husky lilt when his character serves as a narrator, and at other times lurking in the background, a melancholy and enigmatic figure.

Ultimately, these performers are overwhelmed by the play's scope and messiness. Still, Coy (whose "A House in the Country" won the Charles MacArthur Award for outstanding new play in 2001) and the Keegan deserve credit for adventurousness: Donn Byrne is not a household name. And on some level, you have to admire "Island's" aching romanticism. If only the play were a little more focused.

An Island of No Land at All: The Story of O'Malley of Shanganagh, by Peter Coy, based on the works of Donn Byrne. Directed by Mark A. Rhea. Costumes, Maggie Butler; lighting, Dan Martin. Approximately three hours. Through July 10 at the Clark Street Playhouse, 601 S. Clark St., Arlington. Call 800-494-8497 or visit www.boxofficetickets.com.