This is Arthur C. Clarke at his stellar best! Aliens resembling the devil land on Earth and everything changes. Religion is gone as well as man's place in the universe. One man tries to unravel the mystery of Earth's new masters. But it is the equivilent of trying to get a dog to understand nuclear physics.
Clarke's explanation of many of the old legends was probably the first to do so. Would have loved to see this story played out in an episode of The Twilight Zone.