When fourteen year-old Jackson's life is uprooted, he finds his new hometown, idyllic Atavus Falls, under attack. The locals choose to call the threat a rabid bear or mountain lion, but as the killer closes in on Jackson and his family, it comes to light that their 'monster' is actually the product of a sociological experiment gone wrong, an experiment whereupon an unhinged psychologist raised a feral child, a child completely deprived of all human contact, in order to prove that language is a contagion, a virus infecting us all.

The fates of Jackson and the monster prove to be entwined at the rootmost level, and Atavus Falls soon shows us that sometimes a monster lives in the soul of a child...and sometimes humanity can be seen reflected in the eyes of a monster.