Meredith and John Dale are agents with the CIA.
I mention Meredith first because she takes the stage first and holds it forcefully for a considerable time, a feat that is not surprising once you meet her as she is a force and a half. And this despite the fact that our initial encounter with her sees her flying back from the Middle East in what she considers disgrace over a blown op. She had been trying to stop the sale of a very nasty biological weapon and her asset to achieve this was snatched off the street in Dubai before she or anyone could stop it and now the kidnappers, probably Russian SVR agents, had him and the $2m CIA dollars he had been given for the upcoming trade. Meredith is both angry with the world and certain she was being flown back to Langley to be canned from her position as a department head in the Counterproliferation Division.
As for John, her ex-husband, he was already canned some time back, forced out and branded persona non grata by the upper echelon of the Agency. The why is pretty important but takes a while to be explained but the sum of it all is that he has been unceremoniously kicked out and told to never come back; that and his passport was confiscated and he was ordered not to leave the country.
This stark treatment of her ex
is why Meredith is so stunned when instead of being fired herself upon her recall to headquarters, she finds that they want to put her in charge of a different, even more important project. The catch to her 'salvation' and reassignment is that for this new project, John Dale's assistance is vital and it will fall to Meredith, his ex-wife, to convince him to put aside his considerable amount of bad feelings and return to a place that branded him a traitor. Not the most auspicious start to a new job for either of them.
Both Dales are in their forties. Quite a few years before when they were still fairly young, Meredith had been the handler for a more rookie operative John and they hit it off immediately. A brief but heated relationship was followed by a wedding and then by a child but the marriage would survive. When we find the two of them reunited, there has been some time passed since their separation. Now they will have to determine whether they can work together again and what that will do to both of them.