The super-smart Deborah Cahn is showrunner for “The Diplomat,” a slick political thriller series, and her skills with plot and dialogue shine out. The show’s premise is sweet: a highly experienced field diplomat is rushed to become the new ambassador to England, finds herself immediately enmeshed in a ship explosion with mysterious origins, and needs to navigate her two worlds while coping with a charismatic, devious husband who has been more senior, including an ambassador’s posting himself. The plot is suitably byzantine, the scenes are immaculately unfurled, and the tension is tangible. Ordinarily, we would expect this to be a routine Netflix thriller, that is, entertaining and proficient, but what distinguishes The Diplomat from most others is the roster of actors. All the many key characters are wonderfully cast and employed, but the standout is Keri Russell in the star role. She is flawlessly magnetic, making the most of a snappy script with terrific dialogue. Hopefully Season 2 will follow apace.