“You picked a side after 9/11. I didn’t have to. It was picked for me.” So explains the protagonist in Mira Nair’s new political/psychological thriller about a man whose world was changed in a day. Narrated in flashbacks, The Reluctant Fundamentalist shows Pakistani native Changez Khan (Riz Ahmed) as an up-and-coming Wall Street whiz kid who loves his adopted country, including the ruthless winner-take-all mentality his job requires. Then 9/11 happens; he’s subjected to knee-jerk bigotry at work and humiliating strip searches at the airport, and begins to question where his loyalties lie. As the film opens, he’s a professor in Lahore, suspected of anti-American leanings. We watch him tell his story to a journalist; the stakes are high, since he’s implicated in the kidnapping of an American colleague. While the film occasionally veers into didacticism, its did-he-or-didn’t-he plot is gripping, and Ahmed gives a subtle and compelling performance.