The A.B.C. Murders by Agatha Christe

       Hello, I am reading a book called "The A.B.C. Murders " by Agatha Christie. In it, I am about 70/228 pages in. The protagonists are Captain Hastings, and Hercule Poirot. They don't really say much about their appearance or anything in this book. I know that Captain Hastings likes to point out the obvious. Poirot a little off his rocker, but he has a lot of character. He has a very interesting mind. He's not really crazy, it's just that he is smart. Here's a quote from the book:
   "Dear me, "I said, recovering from the shock. "I suppose next time I come home, I shall find you wearing false mustaches---or are you doing so now?"
    Poirot winced. His mustaches had always been his sensitive point. He was inordinately proud of them. My words touched him on the raw.
     The antagonist is someone called A.B.C, I haven't figured out who it is though, I know that he/she sends letters to Hercule Poirot and Captain Hastings, and tells them where the next person is going to be killed.