The answer would be a catalyst. Someone or something who causes something to happen.
They are different because the reader is job is to read the text and give it the emotion and excitement and drama. The writer just needs to write a good text make sure it has a good intro and a fitting body that way the conclusion will leave us with a lot of emotions that way the story is phenomenal the reader gives all he can and the writter can be proud of his work.
Answer: mysterious? No form actually goes with it-
He’s angry because the men didn’t arrive yesterday like they should’ve. Hope this helps!