An abused young man changes factions, to become a strong but vulnerable leader, while trying to hold on to his values as ambitious leaders prepare to take over.
The story of Four is an interesting one, worth telling. The series of novellas that make up this book are informative in their own way, but I don't find even the first one, which tells of Tobias' choice to leave his father and Abnegation, to be even close to the emotional attachment that Tris' similar story has in Divergent.
We know almost all of Tobias' background from the other novels, so this was just to fill in the details. While I didn't recognize it in the trilogy, Tobias is quite damaged, due to the abuse he suffered under his father's hand. The story is told again from the first person perspective, which gives it some emotion, but Tobias has hidden himself, even from himself. Because of that, he doesn't have the range that Tris has.
The initiation routine is a little different from what Tris goes through, and I didn't think it showed enough of how Four got his expert abilities. It focused more on the fear simulations. As he gets older and becomes a member of Dauntless, we see the conspiracy between Jeanine and Max, and the part Eric has to play in it. There was no reason for us to know that Eric was a plant from Erudite in the main trilogy, so that provides us with some interesting information as to his motivations in the other books.
It's obvious that Four is ready to abandon Dauntless soon, until Tris arrives, and he sees something special in her -something that completes him. He doesn't want the Dauntless leadership because he might meet his father in council meetings. It's a simple a reason as that. Tris helps him face that fear, and that's what helps make him a better leader by the end of the trilogy.
The story focuses around the conspiracy, and Four's efforts to learn more about it. He gets hints, and he knows that something is going to happen soon. He even goes to warn his father, who although he rejects Tobias, probably takes note, which is how he and the other leaders survive. There are a couple more scenes that overlap with Divergent, but told from Tobias' perspective. It's obvious that he's drawn to Tris long before she's drawn to him.
Unfortunately, the conclusion to Tobias' story is told in Allegiant, so this book doesn't get any kind of wrap-up. It might have been more satisfying if there was one more story, told after the final events of Allegiant. As it is, though, the stories were informative and allowed us to see Four in a different way, as somebody who needs help and attention, is careful around love, and who is trying to fit in where he shouldn't.