Grass by Sheri S. Tepper (originally published 1989, Doubleday; later reprints by Bantam and Orion) is the first novel in the Arbai trilogy. Set on the planet Grass, it explores themes of ecology, colonization, and human survival. The lush world is dominated by mysterious native life forms—horselike creatures and other alien species—that play a central role in the unfolding mystery. Humanity, threatened by a deadly plague across the galaxy, seeks answers on Grass, where secrets of coexistence and hidden dangers emerge.