If you haven't read the previous posts about the Hunger Games then I would encourage you to read them before reading this. I wouldn't want to spoil the story for you! : )
In this book Katniss is now living in District 13, along with the survivors from the previous bombing in District 12. Katniss and some of the other were taken from the Hunger Games to District 13 but Peeta wasn't one of them. He had been taken back to the Capitol. After much time after her recovery, Katniss decides to be the Mockingjay, the figure head of district 13. In return she gets immunity for her friends and permission to be the one to assassinate President Snow. One of Katniss' main jobs for being the Mockingjay is staring in commercials for the rebel side. While shooting a commercial in District 2, where war is currently going on, Katniss and her friend Gale, witness a small but crowded hospital get destroyed by the Capitols bombing. Because district 13 is gaining strength, the Capitol decides to release footage of Peeta being tortured. Later district 13 views footage from Peeta. While talking he quickly mentions that the Capitol is about to bomb District 13. Right away everyone in district 13 is sent to the lower living areas further in the ground, as far away from the bomb as possible.
Later Katniss requests that District 13 sends out a team to retrieve Peeta from the Capitol. When Katniss finally sees him after what seems like a life time, instead of a hug, Peeta tries to choke her. Later they find out that instead of any physical torture, the Capitol "hijacked"his memories of Katniss, making him believe that she was a demon. To help Peeta recover, the doctors in 13 help him remember things about Katniss that the Capitol didn't know about. Soon Peeta and Katniss are able to stay in a room with eachother without him trying to kill her. Katniss feels that while there is a war going on outside she isn't doing anything to help. So President Coin (president of 13), puts Katniss and a few others through training. Later Katniss and Gale are put on a team along with other victors that made it out of the Quarter Quell. With a few last minute adjustments, the team finds out that Peeta will also be joining them. To find out what happens next to Katniss' team in the fight against the Capitol, read this great book!