Albert's speech about the graves in the town plaza, and his utter moral outrage at the people trying to film the FAYZ at the end.
Caine's letters. Especially the second one. And Diana's reaction to it; "She read it again and again. Each time crying. Each time laughing." It's a little too much to handle.
Sam and Astrid inviting Diana to live with them. After all she's been through, it looks like Diana has finally made some genuine, real, healthy relationships which aren't bore out of manipulation. Seeing just how much she has grown since book 1 is heartbreaking and beautiful.
Poor, poor Dekka Talent. She lost the woman she loved and her parents still don't accept her.
The most painful moment of the book for Dekka (and possibly in general) is her reaction to Brianna's death. She's cradling Brianna's body and crying into Edilio's shoulder, and Edilio, who also believes the person he loves to be dead, has no choice but to force her to suppress her emotions so that she can keep up the fight against Gaia.
The revelation that both Caine and Sam were in fact, legitimate, despite Connie's suspicions.
Sam: But that means Caine lived his entire life without... Astrid: Without love. Sam: But not in the end. In the end he found it.
Just this effing line; "Turn out the light Sam."
And also; " You are now free to leave the FAYZ."
Hunter in PLAGUE. Actually, Hunter all the time.
A running motif in the series is Sam mentally putting himself on trial and wondering what he would say to the adults if the FAYZ ever came down. How could he explain why their children are battered, starving, and traumatized, or why the town is burned down and in ruins, or why there's a large graveyard in the plaza?