Tom Burke, Naomie Harris and Pierce Brosnan also feature in a coolly cerebral take on British espionage from Steven Soderbergh

There is no physical embodiment representing the title of Steven Soderbergh’s “Black Bag,” duffel, burlap or otherwise. It is instead conceptual, a stop sign between lovers who happen to be spies. “Where are you off to tomorrow night, darling,” one might say. When “black bag” is the answer, the conversation ends right there, no questions asked. The cold, efficient and really British spy thriller stars a marvelous Michael Fassbender (“The Killer”), a sly Cate Blanchett (“Tár”) and an underused but most welcome Pierce Brosnan, who all help overcome a ridiculous premise. When a secret that could trigger a nuclear explosion in a foreign country is found to have been stolen, likely from the inside, Fassbender’s George Woodhouse is charged with rooting out the traitor. There are six suspects, including George and his wife and fellow agent Kathryn (Blanchett). But the other four are also couples who each work for British intelligence, which would seem like a real security risk, if not an HR problem. They are Col. John Stokes (Regé-Jean Page of “Bridgerton”) and the MI6 psychologist, Dr. Zoe Vaughan (Naomie Harris, Moneypenny in the Daniel Craig James Bond films); along with insecure agent Freddie Smalls (Tom Burke) and computer surveillance specialist Clarissa Dubose (Marisa Abela, who played Amy Winehouse in “Back to Black”). In an early unconvincing sequence, George invites them all to a delicious dinner he has cooked himself for “fun and games” and proceeds to easily get these trained agents to spill secrets about their significant others, a scene climaxed by Clarissa driving a steak knife through Freddie’s hand. Other than that, there isn’t much action in “Black Bag,” which is not a complaint. It plays as a rather intriguing chess match as George attempts to root out the traitor. Pressure is on from his boss, Stieglitz (ex-Bond Brosnan, who makes the most of his underwritten part), especially when evidence seems to indicate Kathryn as the traitor. He’d love to ask her about it, but black bag, you know. What puts the movie over the top is that George, perhaps named after novelist John Le Carre’s famed cold fish spymaster George Smiley, is beneath the meticulous cool in love with Kathryn. One gets the impression that if Kathryn is the mole, George would rather go down with her than turn her in. That’s probably the hook that got the prolific Soderbergh, whose horror film “Presence” hit theaters in January, interested in the project. He makes the most of it, overcoming the ups and downs of David Koepp’s script. They say that all is fair in love and war (even a cold one). In “Black Bag, it leads to a mic drop of an ending.