When Aaron Hotchner, Spencer Reid, Emily Prentiss, and Derek Morgan are taken hostage during a joint operation, the only one sent to retrieve them is a cold, highly trained agent from another unit—someone even her own team fears. She’s lethal, silent, and unstoppable. But once she joins the BAU, one thing becomes clear: the only thing more dangerous than her skills… is how close Spencer Reid is getting to breaking through her walls.