Will is a fraud. Olivia is a wreck. They meet at a grief share group and quickly bond over their brokenness. They also have a peculiar hobby; they seek out sickness. Will hunts for the latest strain of flu. Olivia doesn't feel comfortable in her body if she isn't suffering from a fever. They become virus chasers, finding confidence in their ability to conquer every affliction they come across.

They soon discover an online community of chasers called The Source and realize that their hobby isn't all that odd when seen from the right distance. And then the mysterious Zaff literally walks into their life, claiming that he has the goods, knows where the latest outbreak will drop. Intrigued, Will and Olivia decide to take their hobby to the point of obsession, believing that if they can conquer the newest strain, nobody can hurt them.