Shay believes she is a carrier of a deadly disease. She survives the Aberdeen flu only to surrender herself to the goverment and unwillingly become a test subject in an effort to find a cure. With the help of the mysterious Dr. Alex Cross, Callie's father, Shay and other survivors will attempt to escape.

Meanwhile, a heartbroken Kai joins up with the lovely Freja who is also being hunted because of her special abilities; they race to find Shay before vigilante hunters find her first. Kai's sister, Callie, continues to hide a secret--she is the true carrier, and her goal is to find the man who killed her and make him pay.

As they fight for survival, loyalties are tested. Is Callie who she says she is? Should Shay trust Alex, the man her mother ran away from--a man Kai hates? Will Kai forgive Shay for her betrayal? Only one thing is certain: they are stronger together.