The oldest aims to become the top jazz clarinetist of the swing era. The middle sibling is impersonating an aristocrat. And the youngest is haunted by a famed poet's ghost.

Martin, Francis and Michael Dempsey — distinctive Irish brothers who have reunited in New York City — are the central characters in Brendan Mathews' debut novel, "The World of Tomorrow." It's June 1939, and within a week, one goes missing, a second sets out after him and a third is dragooned into a conspiracy that might "send history careening in unforeseen directions."

Mathews' characters are likable and clever. His plot, rife with geopolitical intrigue, is nicely calibrated. And he packs his debut with period details that evoke the vibrancy of the Savoy Ballroom and the magnificence of the then-new RCA Building (now known as 30 Rockefeller Plaza). For all its strengths, though, this is a good novel needlessly stretched to 500-plus pages.

At the heart of the action is an unexpected family get-together. Eldest sibling Martin has been in New York for a few years, trying to make it as a musician. On a spring day at the end of the Depression, Martin's brothers arrive bearing bad news: Their father has died. Martin is surprised, of course, but the bigger shock has to do with the messengers. The last he knew, Francis was in prison and baby brother Michael was a seminary student — both in Ireland.

How did they get here? Granted day passes to attend their father's funeral, Francis seized the opportunity to escape, bringing Michael along with him. A friend steered the two men to a hideout, which turned out to be an Irish Republican Army safe house. There, a misunderstanding took a tragic turn, with Michael injured by a bomb blast. Ever since, the bookish youngster hasn't communicated with anyone but the ghost of William Butler Yeats.

Francis, meanwhile, has found a fortune stashed at the safe house and intends to use the money to forge new identities for Michael and himself. For a time, they pretend to be Scottish royals. Soon, however, an IRA hitman hunts them down. The thug informs Francis that his family will suffer unless he commits an act of political violence at the ongoing World's Fair in Queens.

The World of Tomorrow, by Brendan Mathews

Although the proceedings call to mind a cinematic thriller, there's plenty of comedy. The Michael-Yeats story line is a daffy one, and Mathews, to his credit, treats it as such, casting the poet in the role of acerbic codger. When Michael's first romantic encounter seems imminent, Yeats says, "I'll excuse myself, though I don't imagine it will be a lengthy absence."

Mathews writes extraordinarily well, but he has a habit of interrupting himself with protracted digressions that add many extraneous pages. Even bit players get lengthy back stories. Midway through the book, for instance, we meet a doctor who has a tiny role — but that doesn't stop Mathews from detailing the physician's family tree, newspaper-reading habits and digestive frustrations.

As for Mathews' main characters, they're Depression-weary, ready to transcend "the sordid history of the Old World and looking boldly to the future."

This is an expansive theme, and from it, the first-time author has carved a commendable novel, even if it's not the epic he'd like it to be.

Kevin Canfield is a writer and critic in New York City.

The World of Tomorrow
By: Brendan Mathews.
Publisher: Little, Brown, 549 pages, $28.