"The Walls of the World" is the first of two novels written by James Tiptree Jr. While Dr. Daniel Dan oversees a long-planned telepathy experiment on Earth and battles his own inner demons, Tivonel, a ray-like being, returns to her home planet Tyree. There, she soon learns that her world is threatened by a massive, all-consuming destroyer that drifts aimlessly through space, devouring one galaxy after another. However, hope appears on the horizon when some inhabitants of Tyree teleport to join Dr. Dan's group. Against the will and ethos of their ancestors, they commit a form of life theft by infiltrating the bodies of the Earth telepaths and transferring their consciousness to Tyree. Humans and Tyreeans come to know each other and now fight together against the great destroyer.