I never know what I'm going to get when I hit the second in a dystopian trilogy, but this I loved. 
 Tris Prior is messed up--her parents are dead and she just killed one of her best friends in order to survive the massacre in Abnegation. 
 Now she must survive at all costs...why? What meaning does her life hold? 
 Honestly she'd rather be dead, and I can almost empathize. 
 Yes, she has Four/Tobias but he is often distant. Dauntless has fragmented into independent and Erudite-bound factions and she doesn't know who to trust. 
 First Amity turns them out, then Candor. Erudite hunts them, and Abnegation is a shadow-faction following the massacre. The loyal Dauntless develop new leadership and seek an alliance with the factionless in a bizarre twist that ultimately makes complete sense. In order to spare her comrade--who are still under Erudite remote-control, Tris turns herself in to be the guinea pig for all Divergent. Subjected to repeated testing it becomes clear that Tris' mind won't break though her body reaches its limit. 
 Still, Tris doesn't think the objective of taking down Erudite for the sheer necessity is exactly the right way to go. And she allies herself with Marcus against Tobias in the final battle. 
 When the chips fall, it is Tris' bravery that might save Dauntless from its own captivity, but then again, I guess we need the third volume to answer that question.