Returning from a planet with both a civilized and a primitive side, all but two of the team become infected and spread a brutal virus. Will Teal’c and Jackson find the cause, or are their colleagues doomed to become Stone Age primitives? [Edit]

Col. Jack O'Neill and the SG-1 team head through the stargate to a planet known as P3X-797 and discover a world divided into a dark and light side, with a population similarly split between the Touched and the Untouched.

The Untouched, who live on the bright side, are humans, a Bronze Age people who seem almost like the Minoan civilization of Earth. The Touched, who live on the dark side, are heavy-browed primitives with limited skills and the brutal instincts of animals.

The findings would be of only academic interest, but when the SG-1 team return to Earth, all but Teal'c and Dr. Daniel Jackson begin a startling transformation: They develop the heavy brows and act with the animal brutality of the Touched. Worse, so do many others at Stargate Command's mountain headquarters, including Gen. Hammond.

As order breaks down and the project is jeopardized, Jackson and Teal'c head back through the stargate in an attempt to discover the reason for this mysterious transformation. Is this a disease that can be cured — or are O'Neill, the general and the others all doomed to live out the rest of their lives as throwbacks to the Stone Age? [Edit]