In this follow up to Chariots of the Gods Daniken looks for evidence of aliens' past visits to earth by examining archaeology. Many cultures from the past show rays projecting from the heads of the people they portray. Large carved rocks are hard to explain. Using technology of the time they would have been very tedious to erect.
Throughout the book Daniken asks, "How could they do this without help from aliens?" or "Is this a carving of an alien?" Sometimes his analysis of what he finds is way off, as when he describes a carving of a person inside a carved circular decoration and captions it as a person in a "spherical spaceship" Art historians can have a laugh at Daniken's expense.
There is good archaeology here. The book is a fast read with many illustrations to back up points.
This book was later republished as Gods from Outer Space.