Kimball Kinnison and the Galactic Patrol again take up battle with Boskonia. The warfare leads to some odd corners of the universe and some stranger worlds. They include the planet Lyrane where a matriarchal society exists and the frigid world of Onio, with its incredibly alien inhabitants.

Twenty years have passed since the events in Second State Lensman. Kimball Kinnison and his wife, Clarrissa, now have five children - the "Children of the Lens". As the offspring of generations of selected matings, they are the most brilliant and capable minds in the universe. Their mission: to conclude the Boskonian war.

In the not-too-distant future, while fleets of commercial space ships travel between the planets of numerous solar systems, a traveler named Virgil Samms visits the planet Arisia. There, he becomes the first wearer of the Lens, the almost-living symbol of the forces of law and order. As the first Lensman, Samms helps to form the Galactic Patrol, a battalion of Lensmen who are larger-than-life heroes. These soldiers are the best of the best, with incredible skill, stealth, and drive.

The Galactic Patrol's Lensmen are the most feared peacekeepers in the galaxy. The "Lens", a telepathic jewel matched to the ego of its wearer, is the ultimate weapon in the war against the merciless pirate Boskone and his forces of lawlessness. The only problem is the Galactic Patrol isn't sure how to capitalize on the Lens' incredible powers. But new graduate Kimball Kinnison is determined to learn.

Written in two parts, Triplanetary introduces the concept of two warring alien races: the Arisians and the Eddorians, whose battles on Earth are unknown to the human race, and in fact the humans are unaware that the Arisians have been secretly and selectively breeding the humans to use as weapons for these battles. From the time of Rome to World War II, the author takes the listener on a lightning-fast journey through Earth's history as the warzone for aliens.