Conquest Over Time by Michael Shaara, Science Fiction, Adventure, Fantasy

"Now this here planet," he said cautiously, "is whacky in a lot of ways. First of all they call it Mert. Just plain Mert. And they live in houses strictly from Dickens, all carriages, no sewers, narrow streets, stuff like that." But that wasn't all. . . . Travis, in reaching Diomed III before any others, found himself waging a one-man fight against more than this; he was bucking the strangest way of life you have ever heard of! What was the startling secret of Diomed III that almost caused Travis to lose his life? And who was Lappy. . . ?