Series is based on two spy's being recruited by a intelligence agency to work together and pose as man and wife. What made the show exceptional was this: They were career spies, who had worked for various unnamed agencies in the past, possibly at cross purposes.
While they are eager to get the job done and learn to work together and trust each other, they are careful to avoid exposing their true identities, past accomplishments or special skills - because these are the secrets a spy lives by and the last person you want to give that information to is another spy you may be working against the next time around.
So you end up with a show full of undercurrents as they get to know each other and respect each other as equals. Who is this person? Did I ever run into them in the past without knowing it? Did I ever get in their way? Did they ever get in mine? Where have I seen that technique before? Was he/she there? Does he/she have info about something that happened that I never resolved to my satisfaction? It's been so long I don't remember specific episode plots or details about their pasts, but the undercurrent of curiosity about the other person battling each characters need for secrecy was what I remember most.
