As others have noted, a clear set of plot points drive the action in this novel. As the story opens, Montag believes himself contented with his life. He enjoys watching things burn, which makes his career as a book burning firefighter satisfying to him. His job is high status, which also adds to his surface sense of well being. He has the outward attributes of a successful life, such as a nice house and a wife. But a series of events lead him to reject his conventional life.
Meeting the ethereal teenaged girl, Clarisse, becomes the first precipitating event that causes him to start questioning how happy he really is.
A second event, close on its heels, is coming home to find out that Mildred has attempted suicide. These two events, so close together, upend his settled beliefs about his life.
A third event that inspires him to change is watching a woman whose books they are burning incinerate herself rather than live without books.
A fourth important turning point that symbolizes an irrevocable step into a new life is Montag's taking of a book for his own, which leads to him taking more books.
A fifth event is his encounter with Faber and their decision to sabotage and subvert society.
A sixth act is reaching out to Mildred, trying to interest her in reading. This leads to her betraying him.
Seventh, Montag kills Beatty, finishing off the repressive "father" figure and freeing himself from the bonds to his old life.
Eighth, Montag's city is destroyed in a nuclear blast, and he becomes part of the group of men committed to preserving knowledge.