Back in the 1970s (no later than 1978), when I was a kid, I ran across a copy of a Nick Carter - Killmaster novel. I know it was fairly new, because a major plot point is that a character lost friends in the Kent State killings (May 1970). But there are a lot of Killmaster books in that interval (about 50 of them! Nick Carter-Killmaster - Wikipedia). Anyone have a list with plot descriptions - the key element I remember is that the woman Nick is with during the book turns out to be the enemy agent - turned by her disillusion about Kent State.