Jake: Halitosis Frodo's got to be our guy, right?
Sergeant Jeffords: Oh, yeah. "A message in blood" is a reference to book one.
Page 843. After Wendivil betrayed Prince Clevang, murdered him, and used his blood to write letters to his children.
Jake: Do you talk about this stuff with Sharon?
Sergeant Jeffords: No. She hates it.
Jake: Yeah, makes sense.