Picking up exactly where we left off, Tris and Four have managed to stop the Erudite-controlled simulation that had turned the Dauntless into a mind-controlled army. Trouble is, quite a lot of the newly awakened Dauntless have decided to stick with Erudite anyway to continue their assault and so Tris, Four and their small band of survivors have nowhere left to turn but to the remaining factions, Amity and Candor. Asking a bunch of peace-loving stoners and people who can't lie to harbour fugitive goes about as well as you'd expect, however.
Also seeking shelter for a spell with the factionless, it's not surprising to find that the people most oppressed by the faction system have had it up to here with it, and would quite like to bring about a change in regime. Which they plan on doing by destroying the information that sparked Erudite's war against Abnegation - information that confirms there's a whole world outside their gates, one in which the Divergent will play a big role.
Suffering slightly from second album syndrome as it tries to tell us the middle of a story, I also found Tris a little more annoying this time around. A lying liar who wants to die, she's apparently no longer able to so much as touch a gun due to her guilt over events in the last book, but isn't about to let that stop her from trying to win the Martyr of the Year award by continually throwing herself into dangerous situations. She's just doing it without any weapons now.
Still, with the big 'reveal' (which wasn't much of a shocker, to be honest) I'm still into this enough to jump straight in to the next book.