Its the 75th annual Hunger Games which means it's time for the third quarter quell ( a new challenge faced to the games every 25 years) and the challenge this year is that the remaining pool of victors from each district will be reaped; Katniss is the only female tribute to ever win the games in district 12 which means she has no choice but to go back to the arena.
The 75th Hunger games is in session and Katniss and Peeta have established their allies. Finnick and mags. Johanna, Beetee, and Wiress join the alliance later in the games.
People are dying left and right and with the little bit of consciousness Katniss has, she shoots the force field. The arena is blown up and half of the remaining tributes are captured by the capitol while the other half(including Katniss) is taken by a rebel group, planning to destroy the Capitol.