These books by DeMille must be sleepers or something. I started with The Lion's Game and was hooked on the NY cop character, John. I am a history teacher and practically live in timelines, so I am constantly reminded about the real events in America as I read. You will enjoy The Lion's Game. I, too, read Plum Island last, but I do not feel that the plots were ruined, in fact it may have been that I was more comfortable with the characters and enjoyed them more.
On DeMille's website he states that his next book will treat the CIA kinder, since he worked them over pretty badly in these three. Who would be good actors for John and Kate in the movie version?
I enjoyed all of Dan Brown's book, as well, especially Angels and Demons.