“ Black Bag ,” an elegant, quick-witted new thriller that finds Cate Blanchett and Michael Fassbender playing married spies, isn’t the pair’s first time together on screen. That honor goes to 2017’s “Song to Song,” one of Terrence Malick’s most intangible and head-scratching offerings — though the two stars can barely recall that experience.

Michael Fassbender is a British spy hoping to identify an agency mole who may, in fact, be his own wife (Cate Blanchett) in a thriller from Steven Soderbergh.