Grounders and Arkadians are warring clans living in the same vicinity. What happens when Clarke, a young prisoner is sent to Trigeda to kill the rival Commander, and ends up falling in love. Does she kill the Heda and earn her freedom, or does she betray her friends and family and fall in love with the young girl with eyes the colour of the forest.

Clarke and Lexa's story continues as they battle new enemies and fight to maintain the alliance.