Cassava is a Black Sin-an undesirable from society that has been trained as an assassin.

She goes where the Priests tell her and kills who they deem unworthy. But this next target is one that stops Cassava cold in her tracks; it's not the usual mark she has to take down. The Priests have learned of someone who is able to weave magic-something that shouldn't be possible, and something that needs to be controlled or eliminated. And to take care of this problem, the Priests are sending her to the mainland, a place forbidden to Cassava and her kind.

When she finds this girl who can weave magic, Cassava is immediately attracted and insatiably curious. She's also overwhelmed and in awe of the mainland, by how much more free and open and safe it is compared to the Islands. But that safety and openness is deceptive as her crush-the girl who weaves magic-soon goes missing, and in her search, Cassava unearths dark truths about the mainland.

And only someone like Cassava-a Black Sin-can do something about it.