Is Marine Sergeant Nicholas Brody a patriot or a terrorist? This is the main question posed by the new Showtime series Homeland. Along the way, it asks a lot of other, more important questions. What are our criteria for deciding? What does a terrorist look like? How do terrorists behave? Need they follow radical religious leaders or is it suspicious enough that a man — devoted to country, red-haired, lilly-white, not religious — would disappear behind enemy lines for 8 years, only to return an observant Muslim?

Claire Danes plays a CIA officer named Carrie Mathison who spent five years in Iraq and is now “in the penalty box” as an analyst with homeland security after being caught inside an Iraqi jail extracting intel from a man who was about to be executed. The intel she gets: “An American prisoner of war has been turned.”

This means very little to Mathison until Brody (played brilliantly by Damian Lewis) is found, alive, under suspicious circumstances. Her bosses at Langley want Brody as a propaganda piece, and she doesn’t have the clout to surveil him legally, so she does it illegally.

Last week’s episode exposed a hole in Mathison’s surveillance (Brody’s garage), and contained a scene where Brody wandered around a hardware store for a day, flipping switches and examining parts. He came home with a rug and, the next morning, in the garage, secretly, he faced east and knelt to pray.

Again we ask: does conversion to Islam make Brody a terrorist? Does hiding the fact? Or is Sgt. Brody just aware of how such a conversion will look?

Making the lens through which we view Brody an intelligence savant like Mathison — who battles an unspecified illness ranging from extreme anxiety to schizophrenia — forces us to question our own reactions to Brody.

Are we witnessing the groundwork of a double agent and a terrorist, or a man who just wants to get his life back and can’t figure out how? More importantly, is our national obsession with security a normal reaction to what we’ve been through, or the very definition of insanity?

These questions needn’t be answered in the show. They’re best left to each viewer. The fact that they’re being asked at all makes Homeland a thriller in the best, most thoughtful sense —the kind where as much turmoil happens in your gut as onscreen. (Showtime, Sundays, 10pm)