R15 (R-Naught 15): A mathematical term estimating how many can be infected by an individual carrying a contagion. Above R1 can cause an epidemic - especially if there is no cure.

Everything is perfect: Their house, their careers and their beautiful daughter. But suddenly it all changes and Walker finds himself attempting to make sense out of chaos as he fights for his very survival amidst the immersion of an unknown, deadly virus. As he tries to maintain his humanity while in the middle of utter world-wide chaos, he struggles with the fact that everything he loves and holds dear has been destroyed by something he can't even see or hear.—anonymous