From the atomic age in Atlantis to the far-flung future, here is a story of interstellar war with Earth as the prize for the victor. The elder race of our galaxy, the Arisians, using advanced mental science, has foreseen the invasion of our universe by the evil Eddorians. The Arisians begin a breeding program on every world that can produce intelligent life, the goal to produce super warriors who can repel the Eddorians. Triplanetary is the early history of that breeding program on Earth, illustrated with the lives of several warriors and soldiers. It ends with the discovery of the interstellar space drive, formation of the Galactic Patrol, and the first Lens-an Arisian device that provides its wearer with mind-reading and telepathic abilities-given to the first Lensman on Earth.