The idea was, that one of the conspirators should offer Ed a letter of introduction to Commodore Vanderbilt, and trick him into delivering it.

It would be easy to do this.

But what would Ed do when he got back to Memphis?
That was a serious matter.

He was good-hearted, and had always taken the jokes patiently; but they had been jokes which did not humiliate him, did not bring him to shame; whereas, this would be a cruel one in that way, and to play it was to meddle with fire; for with all his good nature, Ed was a Southerner--and the English of that was, that when he came back he would kill as many of the conspirators as he could before falling himself.

However, the chances must be taken--it wouldn't do to waste such a joke as that.
So the letter was prepared with great care and elaboration.