The Last Agent by Robert Dugoni

 When I requested this book from the library I didn't realize it was a sequel (to The Eighth Sister, which I hadn't read). But I managed to figure out what happened in the first book and jump right into the action.

Our hero is ex-CIA guy Charles Jenkins, who was apparently betrayed by the CIA and tried for treason in the first book. As our story starts, he gets a visit from a CIA guy telling him that the woman who saved his life on his last mission in Russia--thought by everyone to be dead--might indeed be alive and in prison in Moscow. Charles feels compelled to head to Moscow to try and rescue her--even though the Russians are still looking for him and angry that he escaped their clutches on his last adventure there.

It's quite the page-turner. And it ends with a hint that there might be a sequel to the sequel in the works.