Survivor shay continues her long search for Callie, the young girl who has been missing since before the deadly epidemic called the Aberdeen flu swept the land. Shay follows her biological father, Dr. Alex Cross, into the Multiverse compound, a scientific cult in a remote area of Scotland. There she investigates the origins of the epidemic and a possible cure. And she discovers that her father has plans that may compromise the lives of everyone in the community—including her own. Having parted ways with Shay in a moment of betrayal, Kai is still looking for his sister, Callie. He's also helping his friend Freja evade capture—but he doesn't realize Freja failed to deliver Shay's last heart-rending message. It is only when Kai resolves to make his stepfather, Dr. Cross, answer for unleashing the epidemic and murdering millions that Kai begins to make his way back to Shay. And to a final showdown with his stepfather where only one of them will survive.