It means a thorough and dramatic change in something
The prefix in the word inadmissible is -in.
I hope this helps you. ☺
The narrator of the story wonders about happiness. He thinks that if he had money, he'd be happier. Yet after he robs the rich white man, he learns that money does not in fact mean that people are happy. The narrator is left wondering why that is. The story does not necessarily offer a solution rather an anti solution: money will not ensure happiness.
