The first five minutes of Cheryl Coons and Chuck Larkin's River's End suggest an enveloping tale of historical uncertainty that will surge and thrill just as the river rafting that gives this New York Musical Theatre Festival entry - playing at the Barrow Group Theatre - its plot.

Two rafting guides, Kent and Georgie (Warren Kelley and Phyllis Sommerville), who see spectators safely down the Colorado River as it passes through the Grand Canyon, start spinning competing yarns about newlyweds Glen and Bessie Hyde, who vanished running the river in 1928. Their song, "Only the River Knows," flows with mystery and curiosity, introducing two Bessies and two Glens to compete for The Truth. The possibilities seem endless.

As soon as the song is over, so does the show. What could be a vividly theatrical exploration of the Hydes' disappearance quickly becomes a rote rundown of clichéd storytelling. Bessie One (the sharp-tongued and sharp-eyed Tempe Thomas) is a rugged daredevil with a yen for vaudeville stardom, while her Glen (Evan Casey) is practical; Glen Two (Colby Foytik) is adventurous and has something to prove, while his Bessie (Dani Marcus) is homebound and wants him to give it all up.

The rest of the show (over two taffy-stretched hours) follows the Hydes' journey down the river, musing on their potential fates, and finally settling on one that seems both improbable and a cop-out. Interestingly, librettist Coons purportedly rooted it - and most of the other details along the way - in fact. Yet these specifics seldom extend to the songs, which are flooded with generic sentiment. Their titles tell the tale: "One Last Ride," "My Love is a River," "The Perfect Run," and (most wincingly) "Everything Has Changed"; the pallid-poetry lyrics aren't appreciably better.

Larkin's music, however, is full of haunting themes that sound as if they could have been passed down by generations of river folk, and the numbers that respect the Colorado's spiritual power ("Bright Angel," the disquieting finale "Still Waters") are the score's finest. Everything is expertly served with a fun folk trio of an orchestra (piano, violin, and bass) led by musical director Laura Bergquist, and all six performers are tantalizing vocalists whose voices blend in intricately colorful and textured ways.

Sommerville, technically the weakest singer, puts so much scratchy character into her numbers that her turnabout from rough-and-ready know-it-all to sympathetic Earth Mother has an unexpected power. Thomas brings an elegantly woodsy quality to Bessie One, and Foytik solidly realizes Glen Two as an overgrown kid about to give up childhood forever. The others make weaker impressions, leaving their characters as flotsam along the way that doesn't contribute much to our understanding of What Really Happened.

No one, however, completely escapes drowning in this too-ambitious, too-ambiguous story that wants to take a stand without saying much of anything. A single, focused point of view would be better than two indistinct ones, and more interplay among the various possibilities would better capitalize on the theatre's unique ability to play matchmaker between what is, what was, and what never has been. Ultimately, everyone involved in River's End would be best served by paying closer heed to the character of ol' man Colorado and his propensity to just keep rollin' along.

River's End
Barrow Group Arts Center, 312 West 36th Street, 3rd Floor
Thu, Sep. 21 at 8pm
Fri, Sep. 22 at 4:30pm
Sat, Sep. 23 at 8pm
Sun, Sep. 24 at 4:30pm
Wed, Sep. 27 at 9pm
Sun, Oct. 1 at 1pm
For information on performances and ticket sales, please visit www.nymf.org