At first, there was nothing strange about Addie and Eva--two souls born into one body, sharing control of their movements. But there comes a point when children are supposed to settle, and the dominant soul takes over while the recessive soul fades away. Hybrid children are simply unacceptable. After all, hybrids are the cause of the war and destruction that consume the countries outside the Americas. So after years of worries, doctors, and tests, Addie finally settles at the age of twelve. Except that she hasn't, because Eva is still there. For the next three years, Addie and Eva pretend to be normal. But Eva is locked in a body she cannot control. So when they learn that there is a way to let Eva move again, they are terrified of being discovered, but they just have to try.