In the story, Kelsey is a professional blackmailer. He asking Carson, a “client”, for extra payment of $16,940.00. The money is needed for paying Horatio. Horatio was another “client” of Kelsey until the statute of limitations for his crime kicked in. Now Horatio is trying to blackmail Kelsey to get back all money he paid him.
In the story, Kelsey and Carson find that there is a technical problem for Carson to prepare this amount of money and transfer it to Kelsey. So they decide that if Carson kills Horatio, this will solve the problem.
My nitpicking yielded an alternate end.
Carson contacts Horatio and promises him $20,000.00 if Horatio agrees to wait few more days for the money. Carson gets from Horatio a copy of his blackmail evidence. Carson uses it to blackmail Kelsey into ceasing to get money from him. This way, Carson gets off the hook, Horatio gets back his blackmail money, and Kelsey is a bit poorer.