The intriguing premise of “Counterpart” is that reality duplicated itself a few decades ago and everyone has another self. But your duplicate is not your identical. The you of one reality could be a doctor and the you of reality, version two, could be a criminal. It all depends on how your paths diverged. But it’s best not to think too much about it, as the main character “Prime” says, because it could literally drive you crazy. With a commanding performance from J.K. Simmons, fast-paced action and spy thriller suspense, “Counterpart” is at the top of this year’s new shows.

Howard Silk (Simmons) is a mild-mannered bureaucrat who dutifully performs his job at a Berlin-based United Nations spy agency. Passed over for a promotion and caring for his wife who is in a coma, Howard’s life is further turned upside down when he learns that his organization safeguards a passageway to a parallel reality. He meets his almost identical self, referred to as Prime, and is suddenly drawn into a dark and dangerous world of secrets.

Prime is sent to Howard’s reality to stop an assassin who crosses over to kill Howard’s wife but he claims that he doesn’t know why she is a target. And neither do we. But we do know that Prime has told Howard at least one lie. From Howard’s point of view, the situation is a confusing, dangerous mess. Can he trust his other? From Prime’s point of view, it’s steps in a larger plan. The shifting perspectives are effective teasers to a larger mystery.

Visually, the series is shades of grey and locating the action in Berlin gives it a bleak, cold war tone that enhances the atmosphere of spies and secrets. The diverse ensemble cast, including Olivia Williams as Howards’ wife, Emily Burton Silk, Ulrich Thomsen as Aldrich, a hardened spy who leads Howard’s agency, and Nazanin Boniadi as the mysterious Clare, all skillfully contribute to the enigmatic plot. Sara Serraiocco, who plays the assassin Baldwin, is a standout and her scenes with her other self reveal a satisfying emotional layer to the idea of divergent life outcomes.

Academy Award winner Simmons is not a disappointment. He easily switches between timid, bureaucrat Howard who has never fired a gun to confident Prime who dispatches killers without breaking a sweat. Prime cares about Howard’s well-being, despite a clear disappointment in the sheepish man he is and Simmons’ ability to convey this sensitivity makes Prime an appealing character. Perhaps Prime sees in Howard the kind of man he could have been instead of the killer he became. The question of how one’s choice or a series of choices changes a life’s trajectory is a central theme of the series.

Wrapping an espionage story around a double life mind trip, “Counterpart” offers an engrossing storyline that will satisfy both those looking for suspenseful action and those wanting psychological complexity along with their spy thrills.

“Counterpart” is on Sundays at 8 p.m. on Starz.

— Melissa Crawley is the author of “Mr. Sorkin Goes to Washington: Shaping the President on Television’s ‘The West Wing.’” She has a Ph.D. in media studies and is a member of the Television Critics Association. To comment on Stay Tuned, email her at staytuned@outlook.com or follow her on Twitter at @MelissaCrawley.