Only males are allowed to pair off, Finnick and Peeta are married and in love. They take on Katniss as a surrogate to have a kid. Chaos ensues when Peeta realizes he might have feelings for Katniss.
I know it sounds super raunchy but it's a really good writing and new plot line.
I didn't finish it and even though I can guess how it ends, I would love to finish reading it