Sixteen-year-old Sam and her older brother, Matty, are seemingly ordinary teens who have survived the unthinkable-witnessing their mother's murder ten years earlier. But one day when they visit their grandmother in a care home, everything changes. After they learn their grandmother has been repeating the same strange phrase for days that forewarns of the demise of the world, a chain of events ultimately leads Sam and Matty to develop superhuman abilities. They also learn the identical marks on their skin are somehow connected to their mother's murder. Now as the siblings are thrust into a power struggle between the organization trying to protect them, the extremists trying to destroy them, and the mysterious figure who has dangerous plans for them, neither has any idea that a secret is about to be revealed with the power to transform their lives forever.