On his morning bike ride on a local trail, Jerry comes upon a sign warning of a local sighting of a mountain lion. He successfully avoids an encounter with the predator, but as his day unfolds the presence of wildlife in the city becomes more and more pronounced…and more and more suspicious. Animals are found where they have no business being, and the appearances seem to coincide with humans disappearing. Are the animals launching an attack on the humans who are annexing their territory, or is it something more sinister?
As Jerry, the most helpful man they know, carries on assisting others, many of these same people begin to display a disconcerting degree of animal qualities. Are the humans themselves de-evolving—sliding back into their selfish, bestial nature?
Along with his friends, Bernard and Lily, Jerry tries to discover an explanation for these occurrences, attempting all the while to fight off the animal world and cling to the unique qualities that make us human beings.