Doctor Aditya Singh goes to work one day and discovers a deadly virus is taking over the world. At the same time, hybrid children start being born that are half-human and half-animal, with no one agreeing which came first, the virus or the hybrids. Meanwhile, before the collapse of society known as the Great Crumble, a father runs away into Yellowstone National Park with his deer hybrid baby, Gus. Dr. Singh discovers that the first symptom of the Sick is an uncontrollably shaking pinky finger,