A man creates a hit list with a stranger during a drunken night out and must then race to try to save those he marked for death as the bodies pile up and all fingers point to him.

In Host, Missouri, the newcomer vet, Dr Eli Rudkus, is called by a farmer to look at one of his cows. The vet finds a strange parasite in the animal and sends it to the agriculture lab to be looked into. He soon finds another one ...