What kind of a letter did the kidnappers write to Ebeneezer Dorset? What were its contents?

Sam and Bill concoct a surprisingly credible and grammatically correct ransom letter. Ordinarily this would be effective, because it would show the father than he was dealing with intelligent men and not with a couple of ignorant hoodlums. The entire text of the letter Sam and Bill sent to Ebeneezer Dorset is shown below.

Ebenezer Dorset, Esq.:
We have your boy concealed in a place far from Summit. It is useless for you or the most skilful detectives to attempt to find him. Absolutely, the only terms on which you can have him restored to you are these: We demand fifteen hundred dollars in large bills for his return; the money to be left at midnight to-night at the same spot and in the same box as your reply--as hereinafter described. If you agree to these terms, send your answer in writing by a solitary messenger to-night at half-past eight o'clock. After crossing Owl Creek, on the road to Poplar Cove, there are three large trees about a hundred yards apart, close to the fence of the wheat field on the right-hand side. At the bottom of the fence-post, opposite the third tree, will be found a small pasteboard box.
The messenger will place the answer in this box and return immediately to Summit.
If you attempt any treachery or fail to comply with our demand as stated, you will never see your boy again.
If you pay the money as demanded, he will be returned to you safe and well within three hours. These terms are final, and if you do not accede to them no further communication will be attempted.
TWO DESPERATE MEN.

Bill had talked Sam out of asking for two thousand dollars because Bill was having such a hard time controlling the boy who called himself Red Chief that he was already desperate to get rid of him. The ransom letter demanded a reply at eight-thirty that night but gave Ebeneezer Dorset until midnight of that same night to pay the actual money. Sam's intention was to be hiding up in the tree above the spot where Dorset's messenger was supposed to leave the reply; but he gave him some extra hours in which to raise the fifteen-hundred-dollars in cash. Sam wanted to know exactly when the reply would arrive. He did not want to be seen crossing any open space in case Dorset should go to the law authorities and they should have a stakeout waiting. As it turned out, there was to be no ransom money. Dorset sent them a reply at exactly eight-thirty in which he stated that instead of paying them $1500, he would take his son off their hands if they paid him $250.
The story is based on heavy situational irony. The two kidnappers did not foresee what a problem they would have with their hostage. Neither did they foresee how indifferent a father might be to getting his son back. O. Henry may have given the father the first name of Ebeneezer as an allusion to Charles Dickens' miserly and hard-bargaining character Ebeneezer Scrooge in A Christmas Carol.