In an alternate world, society is divided into two classes: the dark-skinned Crosses and the white Zeroes. Seffi and Callum have been friends since childhood—and soon their friendship blossoms into something more. But they can't afford to show these feelings. Seffi is the daughter of a high-ranking official from the ruling Cross class. Callum is a boy from the lower class of Zeroes, former slaves. In a world full of prejudice, mistrust, and class struggle, their relationship is forbidden and risky. Especially when Callum begins to be suspected of being involved with the Liberation Militia, which seeks to overthrow the ruling elite.