Still of Riz Ahmed and Liev Schreiber in The Reluctant Fundamentalist. (Ishaan Nair)

There’s a double meaning to the title of “The Reluctant Fundamentalist,” filmmaker Mira Nair’s great, gripping and complex drama based on the 2007 novel by Mohsin Hamid about the roots of extremism.

On a superficial level, “fundamentalist” refers to religious identity, one unfortunately most often associated with Islamic terrorism these days. And the story — about an ambitious, Pakistani-born Wall Street financial analyst who becomes disenchanted with the United States after 9/11 — certainly suggests that most obvious reading. In that interpretation, the reluctant fundamentalist is an assimilated Muslim forced into anti-American radicalism by America itself.

But the hero Changez Khan (Riz Ahmed), whom we meet at the outset as an older and wiser professor of revolutionary studies at Lahore University, isn’t quite what he appears. The other meaning of “fundamentalist” refers to Changez’s prior life in the states, where, as a young man, he was paid big bucks to fix broken companies, coolly evaluating — and, if necessary, streamlining — a business’s “fundamentals.” That means he was often in the position of having to fire people, a job that might inspire reluctance in anyone with a heart. (The name Changez Khan is a variant of Genghis Khan.)

So, does the ambivalence of the title refer to the ruthless Western capitalist or to the idealistic yet puritanical Pakistani?

The answer, along with several even more fascinating questions, percolates up over the course of a single, extended conversation. As adapted by screenwriter William Wheeler, Hamid’s tale is structured around an interview with Bobby Lincoln (Liev Schreiber), a journalist who suspects Changez of involvement in the abduction of an American academic in Lahore (Gary Richardson). By way of answering Bobby’s questions, Changez insists on telling his story from the beginning, as the film flashes back to his time in New York.

It’s an an engrossing story, bracingly told, and it begins, like many immigrant sagas, with the American Dream: a great job, a beautiful girlfriend (Kate Hudson) and unlimited prospects. But Changez’s dream begins to turn into a nightmare after 9/11, when the bearded, dark-skinned man with the exotic accent is, for the first time, subjected to suspicion and profiling because of bigotry.

It would be easy for the film to rely on shorthand — bullying begets bullying — but Wheeler’s screenplay takes its time, allowing the nuances of Changez’s transformation to reveal themselves organically. Ahmed delivers a riveting performance, making his character’s metamorphosis not just credible, but sympathetic. Hudson is equally good as Changez’s artist sweetheart, a woman with a fascinating backstory of her own.

And let’s not forget Bobby. The reporter Changez is telling his story to has a heck of a lot more to do with the unfolding of “The Reluctant Fundamentalist” than to simply hit “record.” There’s more than meets the eye to this character, too, and Schreiber brings a richly three-dimensional fullness to the role.

As the identities of the two men become more knotty, however, they also become more enmeshed with each other. Although there are times when the movie drags a bit because of all the flashbacks, it mostly maintains a steady forward momentum, chugging toward its exciting, volatile climax. As the film progresses, it begins jumping back and forth between New York and Lahore with ever increasing urgency.

But Nair’s film is more than a thriller. As she proved with 2006’s “The Namesake,” she’s adept at big, sometimes messy narratives that embrace contradiction — emotionally, politically, morally.

“The Reluctant Fundamentalist” will likely make some people mad, because of the way it holds the U.S. responsible for the repercussions of its actions in the world. Like Changez himself, the film has a complicated relationship with the superpower. There’s love there, to be sure. But because there’s love, there’s also the belief — expressed with all the pain and fervent hope you might imagine — that America, and Americans, can do better.

R. At area theaters. Contains obscenity, brief sexuality and violence. In English and Urdu with subtitles. 128 minutes.