This is the sentence I've got problems with. It's a bit dated translation but I believe one of the suggestions I listed below is applicable here.
"What was it had happened to work this revolution in him?"
(these are definitions from Google dictionary)
1. bring into a specified emotional state. "Harold had worked himself into a minor rage" 2. produce as a result. "with a dash of blusher here and there, you can work miracles"