In a slow-burn sophomore season, Jez and John-Henry Butterworth's espionage thriller makes a lot of pivots — away from the mystery in its central romance, away from how much it sucks to be a spy — but its most damaging shift is even simpler: It drifts too far from its star. [Editor’s note: The following review contains spoilers for “The Agency” Season 2.] Late in “ The Agency ” Season 2, Dr. Rachel Blake (Harriet Sansom Harris) stares into the eyes of a Martian and marvels at what she sees.