The basic story: pieces of a gigantic metal robot, thousands of years old, are discovered scattered around the earth, buried deep in the earth or under the sea. Where did they come from? What are they for? A team is assembled in top secrecy to rebuild the robot and figure out how it works. 

The story is told in a series of interviews -- reports submitted by an anonymous interviewer who is pulling most of the strings behind the project. This narrative structure is very easy to follow and pulls you in nicely. I finished the book in a single day.