When a plane crashed in the quaint town of Castor, it unleashed a virus that turned everyone into hissing, blood-thirsty, undead monsters. Monsters that could transmit their plague in seconds, that could run as fast as dogs, and that could fuse themselves together to create massive mutated beasts. Four teens - Connor, Seth, Amanita, and Nicole - fought for their lives to secure vital data from the plane wreckage, some of them paying the ultimate sacrifice.

Now they need to get to San Diego with their secret, but the plague is spreading too fast. They have no friends or family, nowhere to hide, and death lurks behind every corner. Worse, the hissers are evolving, and it may be impossible to stop them at all.