IN THE RADICALLY decent "Brooklyn," a poor, vulnerable Irish girl arrives in America and . . . nothing awful happens.

You keep waiting for folks to exploit poor little Eilis (Saoirse Ronan), but nobody does, and this is somehow transfixing.

The been-around-the-block dame on the boat to the U.S. gives Eilis useful advice.

The priest (Jim Broadbent) who sponsors her is honest, compassionate and helpful.

The landlady (Julie Walters) who houses her gives her the best room and a hilarious floor show with every meal.

The young man (Emory Cohen) who fancies her does not seduce and abandon her.

The frosty manager of the posh department store where Eilis works does not fire her when homesickness wells up and tears run down her cheeks. In fact, she helps the poor girl pick out just the right bathing suit for a big date on Coney Island.

Wait, there's more.

When her competitive, man-crazy flatmates find out she has a steady guy, they . . . help her learn to eat spaghetti for the famly meal with her new Italian beau.

What in the name of "Gangs of New York" is going on here?

More to the point: How, with so little surface abrasiveness and such an absence of apparent conflict, does "Brooklyn" maintain its strong emotional hold?

Well, the movie's placid surface is deceiving. Big things masquerade here as small things. Example: Terrified Eilis, never parted from her sister and mother, asks an Irish woman who's spent time in America about the postal service - will she get her letters from home?

The reply: At first, hardly ever. Then, all the time.

That's a small miracle of economy, poetry and wisdom, and the movie, adapted by Nick Hornby from the Colm Toibin novel, is full of such moments.

And "Brooklyn" - tranquil surface, swirling depths - has the ideal lead in Ronan. Her Eilis is a plain girl with few prospects who leaves County Wexford for the presumed opportunities of New York. She's overwhelmed in this teeming city and behaves like a wary rabbit - as if by remaining still, the world will not notice her.

But folks do. A handsome plumber (Cohen) spots her at a dance and commences an ardent courtship.

Like so many things in "Brooklyn," it changes her. In this new world, all of the old assumptions about her fall away. Eilis does not try to reinvent herself, but it happens. Her intelligence turns to confidence; it shows in her manner, she seems to grow taller. Ronan communicates this quietly and beautifully.

Just as her romance becomes serious, events in Ireland call Eilis home, where she attends to family business, attracts a suitor (Domhnall Gleeson) and allows herself to enjoy the effect her duckling-swan transformation has on those who had overlooked her.

Ireland, Brooklyn, Old World, New World, with an eager suitor to represent each - it could be the stuff of soap opera, but "Brooklyn" operates on a deeper level.

Eilis loves her home, where everthing stays the same - for better, for worse. But she flourishes in the chaos and ferment of America, where nothing stays the same, for better, for worse.

As will one day become clear, the movie slyly notes, to fans of the Brooklyn Dodgers.

Blog: philly.com/keepitreel

Online: ph.ly/Movies