Jake Murdock wants revenge on Parmalee for sending him to prison. His plot involves Dr. Duvain who has a mind-controlling drug that can make a man kill his best friend. To remove suspicion they plan to have a ranger kill the captain. Reese is picked and undergoes a series of injections to prepare him for the murder. A $5 gold piece is the key to controlling Reese, whenever he sees one he is to obey the next verbal command which results in Reese allowing an outlaw to escape, immersing himself in a horse trough (Go soak your head) and busting up the saloon. Chad investigates the doctor's background and reads books about chemistry and the brain. He figures out what is causing Reese's strange behavior and convinces Parmalee of it who then devises a way for the plan to backfire on Murdock and the doctor.
