A pair of time travelers from Earth's distant future are sent back to the past by their superiors on a mission of observation. However, the pair use the trip to plot for the eventual takeover of Earth in the future by wiping out most of mankind with a deadly virus and using the planet of the giants as a staging base. They eventually run into the castaways and use them as unwitting accomplices to their plot. Eventually Steve, Mark and the others find out the pair's scheme and try to stop them before they change mankind's future.
—Brian Washington <Sargebri@att.net>