Insurgent

“Killing you is not the worst thing they can do to you," I say. "Controlling you is.”

I'm actually of the opinion that this sequel is better than the first book. More world-building (exploring the factions/factionless) that was missing in the original, the return of minor characters and much needed character development in general.

It does feel like more of a long bridge rather than a rollercoaster - truly, nothing of great substance happens, but it gets you from the end of A to the beginning of C and does so pretty decently.