Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Initial Situation
From the beginning until Hank and Dagny return from Wisconsin
During this stage we meet most of our major characters, and the main quests are put into motion: to build the John Galt Line to save Colorado and find the inventor of the motor.
Conflict
From Ellis Wyatt's disappearance until the closure of the John Galt Line
Our main heroes are faced with an increasing number of trials, both personal and professional. In this period more businessmen disappear and Dagny is unable to save the John Galt Line.
Complication
From the period where Directive 10-289 is passed until the collapse of the Taggart Tunnel in Colorado
Things seem really bleak here after the disastrous Directive is passed. Dagny quits only to be sucked back into things after the Taggart Tunnel disaster. Hank is meanwhile blackmailed into signing away the rights to his Metal because of his relationship with Dagny. All the major characters seem isolated and beaten here.
Climax
Dagny crashes her plane in Atlantis and learns the truth about John Galt
After an exciting plane chase and crash we get a lot of answers and shocking revelations while Dagny is in Atlantis with John Galt and all the people who have disappeared.
Suspense
From Dagny's departure from Atlantis until Hank leaves for Atlantis
Dagny leaves Atlantis and all the book's major relationships are dramatically changed. Things get worse in the real world and after a lot of trials Hank finally goes to Atlantis, leaving Dagny alone.
Denouement
From John Galt's radio address until his capture and torture
Things start winding down once Galt delivers his radio address. The country's downfall is approaching and Dagny undergoes the last of her trials when Galt is captured. At the end of this stage, she finally decides to abandon her railroad.
Conclusion
From Galt's rescue until the end
Galt is saved and our heroes escape to Atlantis, though not without costs. New York blacks out, the country collapses, and Eddie Willers is left stranded in the wilderness.