Mulder and Scully learn that they aren't the only ones desperately searching for their long-lost son, William. The very fate of the world may depend on it.

When a pair of teenage girls attack one another, each believing the other to be a monster, Mulder and Scully find that their investigation could possibly lead back to their long-lost son, William.

Mulder and Scully rush to find an on-the-run William while the Cigarette Smoking Man pushes forward with his ultimate plan.