What is more psychically exhausting, in fiction and I suppose in life, than the story of the double agent, the mole, the traitor embedded among those he’s working against? It’s a dramatic theme we return to again and again — Keri Russell and Matthew Rhys got six seasons of “The Americans” out of it a few years back. But as a viewer (and perhaps this is just me), whenever characters go undercover, I want them to get along with, even be liked by, the people they’re spying upon, and I’m always disappointed, even upset, when their cover is blown — not for the spies, but for the people whose trust …