How did the kidnappers demand the ransom to the boy's father

After composing a ransom letter that asks for only $1,500, Sam leaves Bill and the boy at the cave, walking three miles to Poplar Cove. In the town, he talks to people until he learns that news of the boy's disappearance has spread. He then posts the ransom letter and returns to the cave to discover Bill and the boy are gone. Eventually Bill emerges from the bushes exhausted and explains that he got rid of the boy on the road to Summit. Bill apologizes to Sam, saying he couldn't put up with pretending to be the boy's horse. Meanwhile, Johnny stands eight feet behind Bill, having followed Bill back to the cave.