Galactic Patrol by E.E. Smith
This is a compilation of several books written by E. E. Smith in the same universe. These books are in the public domain.
The Eddorians, a dictatorial, power-hungry race, come into our universe from an alien space-time continuum after observing that our galaxy and a sister galaxy (the Second Galaxy) are passing through each other. This will result in the formation of billions of planets and the development of life upon some of them. Dominance over these life forms would offer the Eddorians an opportunity to satisfy their lust for power and control.
The Arisians detect the Eddorians' invasion of our universe and realize that they are too evenly matched for either to destroy the other without being destroyed themselves. The Eddorians do not detect the Arisians, who begin a covert breeding program on every world that can produce intelligent life, with particular emphasis on the four planets Earth (Tellus), Velantia III, Rigel IV, and Palain VII, in the hope of creating a race that is capable of destroying the Eddorians.
Samms and Roderick Kinnison are members of the two breeding lines and they are both natural leaders, intelligent, forceful, and capable. The Arisians make it known that if Samms, the head of the Triplanetary Service, visits the Arisian planetary system he will be given the tool he needs to build the Galactic Patrol. That tool is the Lens. The Arisians further promise him that no entity unworthy of the Lens will ever be permitted to wear it, but that he and his successors will have to discover for themselves most of its abilities.
The Lens gives its wearer a variety of mental capabilities, including those needed to enforce the law on alien planets, and to bridge the communication gap between different life-forms. It can provide mind-reading and telepathic abilities. It cannot be worn by anyone other than its owner, will kill any other wearer, and even a brief touch is extremely painful.
Using the Lens as a means to test mental qualities and identify individuals able to help him, Virgil Samms visits races and species in other star systems, recruiting the best of them and forming the nucleus of a Galactic Patrol. Their opponents are discovered to be a widespread civilization based on dominance hierarchies and using organized crime to assume control of new planets.
