The Gatekeeper — David Neth

His enemies are closer than he thinks...When Ash gets a phone call from Detective Jenna Harkness, he knows he's in for a whirlwind. She tells him an officer brought in a crazy man who might be of interest to him.The man thinks it's 1969.But when Ash listens in when Harkness interviews the man -- who identifies himself as Donald Douglas -- he isn't convinced that there's much of a connection. That is, until Douglas lays eyes on Ash and spits in his face. The team soon discovers that Douglas is the latest hitman hired by the Gatekeeper to kill Heat. But they still haven't figured out a way to stop the Gatekeeper and keep him contained under police supervision. And unlike Heat, he's willing to change history to settle the score.