Furthers the plot as the main character is now Divergent, and in her shoes she is now a mixture of Abnegation, Dauntless, and lastly Erudite. This makes her have to decide between the three factions, furthering the plot and causing suspense.
Erudite begins the Plan
Suspense is created during this part of the book because during this part to find the flag, Tris and Four climbs the Ferris Wheel to get the height advantage and find the location of the flag. This develops her character and creates suspense when Four saves her and she learns to trust him.
Hearing Eric and Jeanine
This event both adds suspense and advances the plot. Tris goes up to turn off the simulation to find Four at sitting down and then looking towards her. Four begins to fight her and Tris tries to stop and awaken Four from the simulation. This creates suspense as the readers worry about Tris and if Four is going to hear her. Four awakens from the simulation though and begins to turn off the simulation and saves Caleb. They leave to then go with Caleb to Amity.
Eric puts Serum in Tris
The two parallel plots link when Erudite does the attack on Abnegation so they can overthrow the government. This picture shows when Jeanine changes Four's reality and makes him attack Tris.
We hear from Tris' perspective Jeanine and Eric talking right before she is kidnapped by Peter and Al. This furthers the plot line as we now know that the Eric and the Erudite compound are working together.
This scene shows when Eric puts the serum in Tris after the fear landscape. This is the serum that is supposed to mind control Tris but since she is divergent, it doesn't work. We are shown that Tris is worried about this serum, and it is disguised as a vitamin shot.