The first time Laurie and her dad see the white rider, watching them from the shadows of the trees, he is alone. Laurie is convinced that somehow he is trying to tell them something -- something her dad needs to pay attention to. Is the rider somehow linked to the genetic research into squirrels that Laurie is helping her dad with in the lab? When a second rider with a bloody sword appears alongside the first, and then a third and a fourth, Laurie knows she must try to understand who they are and what they represent. With the help of her brother and his best friend, she discovers what the riders mean, but will it be too late to stop the chain of events that has been set in motion?