A multi-national forestry company engages in genetic experimentation to increase logging yield in a remote section of forest. But the experimentation goes disastrously wrong, transforming a disparate group of loggers and environmental activists into the "infected" -- ravenous, zombie-like creatures who prey upon the few terrified survivors while they attempt to understand and control the disaster...
During the 1967-68 and 1968-69 seasons, the number of shows was reduced to three specials per year before returning to the weekly format on 20 September 1969. During these two seasons, four specials were made.