John Paine is an agent with the CIA.
Paine was an old-timer with the Agency, having served back in Vietnam in the famour Phoenix program where he and his fellow agents went deep into enemy territory to find and eliminate key personnel without warning and without mercy. Paine was one of their best but, in keeping with his penchant for speaking his mind and telling his superiors the truth, not just what they wanted to hear, he was always considered an outsider.
In the books depicted in the series, though, Paine is not just a rogue operative in that he does things his own way, he is truly a rogue agent, namely an agent that has revolted from his superiors and is out on his own, unpredictable and dangerous. He turns rogue when an order to hold or eliminate him goes out from headquarters and Paine has no idea why. He has done nothing to deserve it, being a good and loyal agent for many years. But someone from Langley wants him dead and Paine does not want to be dead. So he goes rogue.
This action, naturally, convinces most everyone at the Agency that he has gone bad. The CIA, fearing that he would head to either the Iron Curtain or worse, to the media, has upgraded the call to a "stop-at-all-cost". Paine, however, isn't as rabid as thought and knows that the real culprit is the high-level official who has framed him. Paine must find him to prove his innocence but he must stay alive to find the proof.
The concept for the series is that Paine was on assignment in East Germany when the mission was wrong and a colleague is killed. Suddenly what little evidence as to what happened points to Paine being a double agent and the order to capture him goes out. When Paine doesn't come quietly, certain that there is a mole, the order is intensified.
The six-book series is a serial with each volume being an episode merging immediately into the next.