Red Flags — Ed Goldberg

Lenny Schneider is hired to protect a client from vague threats delivered with cut-and-paste notes. In the process, he discovers a plot to kill seemingly-random victims connected only by old age. Schneider finds a possible motive in the contents of a long-dead writer's journal, and gets caught in the web of a fifty-year old political vendetta having its roots in the anti-communist hysteria of the 1940s and 1950s. Then he realizes that all the deaths involve the color red.
As he closes in on the truth, his whole life is threatened with extinction, and the Red Scare ceases to be only a term in the history books.