FBI agent Frank LaCrosse arrives in Amarillo and tells Olmstead an elusive serial killer is responsible for the murders. Olmstead discovers that LaCrosse has been taken off the case because the kidnapped boy is his son Andy. LaCrosse has a cryptic note from the killer saying that to find his son, he will have to kill him first. The note includes other clues which are later revealed. LaCrosse teams up with the reluctant Amarillo sheriff's department to continue his investigation. The tactics of the FBI agent concern Olmstead at first, particularly after finding out LaCrosse's personal conflict. He also worries that cooperating with the suspended FBI agent might cost his own job.