Callum is a Nought - an inferior white citizen in a society controlled by the black Crosses. Sephy is a Cross - and the daughter of one of the most powerful, ruthless men in the country. In their hostile, violent world, noughts and Crosses simply don't mix. But when Sephy and Callum's childhood friendship grows into passionate love, they're determined to find a way to be together. And then the bomb explodes...