Everett B Cole: 18 books

Man has developed many a deadly weapon. Today, the weapon most effective in destroying a man's hopes and security is the file folder ... and that was the weapon Morely knew and loved. But there was something more potent to come.

Extraterrestrial explorers to a planet (everyone seems to be human, no one seems to be from Earth) left behind quite a lot of their equipment when they left a few hundred years ago. Now they've come back to fetch it, but the people who found the stuff (telepathy rings, force field belts) have set...