I read recently that it was based on Chapman, and was surprised. It is so good at recreating the atmoshere of the 80s, and accurately depicting the events, it seems like it could be a real story from the 80s. There were a few unrealistic events towards the end (Soviet diplomat assassinated in DC during talks, that would have been a major crisis) but all in all, as a person who studied US-Soviet relations and then worked in Congress on foreign affairs during the 80s, it was very true to life and brought back lots of memories. Those were very exciting times. I imagine there were spies there who were doing similar things then, even if not based on an actual person.