Jess is on the hunt for the next man on his list, Sean Aker. He heads for the town of Lonsdale, Texas, but before he gets there, he ends up meeting a rancher, Olaf Martin, who has hired four top guns.
While visiting the rancher, he finds out that Aker has killed two of Martin’s cowpunchers. Martin tries to pay Jess to go after Aker, but Jess won’t take his money, telling him he’s going after him anyway.
Martin talks Jess into letting his best hired gun, Eddie Pitman, go along with him.
Then Jess is contacted by United States Marshal Frank Reedy. Someone is killing lawmen using a Sharps buffalo rifle, but no one knows who the shooter is.
Jess is tasked with finding out who’s committing these murders of lawmen. Few clues emerge until finally Jess puts two and two together and discovers the killer’s identity.
Strangely enough, a harmonica is the key to solving the murders.
To make matters worse, this is one time Jess finds himself conflicted about killing a killer.