The first section of the novel parallels the start of Keating and Roark's respective careers. When Roark finally strikes out on his own, it represents a turning point in the action.
After setting up Roark's career and the complications that come up at work, Rand introduces love to the mix. At this stage in the game, Roark is battling for both his professional and his love life.
Roark and Dominique start a complex emotional and physical affair in secret while Dominique grows further connected to Peter Keating and Toohey at The Banner. The cast of characters is, at this point, all assembled, and rivalries start to become apparent.
Roark goes to trial over the Stoddard Temple debacle (or disaster) and Dominique marries Keating. Everything sort of blows up in people's faces here as Roark's career and personal life becomes epically stormy. The events in this section impact everyone in the novel, though, not just Roark.
Rather than resolve things, Rand makes them more complicated by having Roark continue to struggle with his career and by having Dominique move on to another man: Dominique and Keating's marriage disintegrates and she ends up leaving him for Gail Wynand.
This book is so long that it has a series of climaxes and denouements and build-ups to new conflicts and climaxes. However, Roark's commission of the Cortlandt House and Wynand and Roark's bromance signal the wrap-up of the novel and pave the way for the conclusion.
Roark blows up the Cortlandt House, goes on trial, and wins both the trial and Dominique. The end.