I want to tell you to step right up to "Agnes Under the Big Top," Aditi Brennan Kapil's poetic meditation on the isolation and alienation faced by immigrants and native residents in an unnamed U.S. city. The play, which premiered Friday in Minneapolis, has a very fine acting company led by Sha Cage, who plays the cancer-afflicted title character whose diagnosis propels the action.

The cast also includes Nathaniel Fuller as heavily accented train conductor Shipkov; Virginia Burke as silent home-care worker Roza, who communicates with birds; Ankit Dogra as conductor trainee Happy; and always estimable Linda Kelsey as a bed-bound character named Ella.

"Agnes" also boasts Andrea Heilman's transporting and impressive set -- a train platform and rail car built out in the middle of Mixed Blood Theatre, with the audience sitting on either side. No doubt her Ivey Award-worthy design and construction was done on the cheap, although it does not look that way.

I want to wholeheartedly recommend "Agnes" to audiences. If it is worth seeing, it is with tamped-down expectations.

While the performances are strong -- hurray for Cage, who is heavily pregnant but pulls off the role with panache, and for Fuller, who gives Shipkov irrepressible heart -- the actual script still needs work.

The playwright's language is smart and often lyrical. She has some clever puns, including on the word "terminal," applied both to illness and transportation.

And Kapil, who also directs "Agnes," is adept at sketching characters. All of those who people this play, including a subway busker played with big-city cool by Nick Demeris, are distinctly evoked.

But the kind of sharpness she displays when limning characters in "Agnes" disappears when it comes to structure. The narrative lacks focus, which makes the play feel slack and meandering. It's a little Samuel Becket-like, a collection of characters waiting for a play.

"Agnes" uses the metaphor of train tracks -- an old comparison -- for people's lives. But their stories mostly run parallel, and don't intersect often enough to create the sparks and fireworks that one sometimes sees when trains rumble in and out of stations. When the characters do cross paths, the stakes are not high enough for dramatic sparks.

"Agnes" feels like a still-being-written illustration of the psychic challenges faced by all people living in a big city, not just immigrants. It asks a lot of important questions: How do you connect with others who may or may not be like you in a big place where anonymity is both a cocoon and its own prison? How do you overcome isolation in a crowd?

"Agnes," which has a lot of promise, only begins to suggest some answers.