He is part of a community that preserves the contents of books before they are destroyed by fire. They possess no books apart from those that are being consigned to memory. The members of the group are the books, and in this way signify their rebellion against the system. As you might expect, most of these outcasts are well-educated, being former professors, doctors etc.
They have their own technology to combat the likes of Beatty and the Mechanical Hound. Grainger has the means to change the chemical makeup of sweat, and they are able to reintroduce long-forgotten techniques such as total memory recall. The reader should not forget the part played in this story by Clarisse. She was the one that inspired Montag into reexamining his life and that of his wife. In fact Clarisse acts as a foil for Mildred. Just as Clarisse inspired Montag, so he now inspires Faber to be more than a pseudo-rebel - to be an activist.
He leaves the city for St. Louis in order to help the cause. The Mechanical Hound is the real science fiction ingredient of this story, part alive, part machine, half dog, half spider, a concoction of copper wire, storage batteries, and blue electricity. It is an ever-present menace throughout the book. It carries a lethal sting in the form of a four-inch hollow steel needle, containing morphine or procaine. Once it has your scent, it will track you down and eliminate you.
It is a development from other such evil creatures, which are found throughout mythology.