What if life on Earth began in outer space? Millions of people accept the theory that intelligent life forms visited Earth thousands of years ago and were worshipped as gods by primitive man. Are monuments like Stonehenge and Easter Island the last remains of an ancient alien visitation? From unexplainable super structures, to knowledge of the solar system, mathematics, and even the ability to make electricity, this special explores evidence of super-human influences on ancient man and embarks on an around-the-world search for answers. It's an investigation into a theory some believe cannot be true, but many agree cannot be ignored.

Tales of angels and giants in the ancient world are examined to determine if the beings stem from mythology or extraterrestrial visits and experimentation on human DNA, and bizarre discoveries around the world may be the key to getting the answers.

Series host and Ancient Astronaut theorist, Giorgio Tsoukalos, explores the mystery of the Nazca Lines found in the desert region of Southern Peru. Hundreds of gigantic lines, some in the shape of animals, geometric patterns and even an alien-like being, extend for miles over a vast section of the arid plain. Scholars are divided as to who built them, and why. Some Ancient Astronaut theorists believe that the massive markings have an extraterrestrial connection, and perhaps the ancient people of the region created these gigantic figures in tribute to the gods who visited them. While the area was abandoned nearly 2000 years ago, remains of ancient Nazca people have been found with strange, elongated skulls. Could this be evidence that there really was contact with "sky people" as ancient legends describe?

Ancient Astronaut theorist, Giorgio Tsoukalos, shares his insight on massive stone structures and strange, giant figures known as Monoliths. What compelled ancient man to move colossal stones, in some cases weighing thousands of pounds, and to build remarkably similar stone monuments all around the world? From the jungles of Costa Rica to England's rural countryside, ancient people achieved extraordinary feats of construction without advanced tools or technology. Is it possible that extraterrestrials instructed the ancients to build these complex structures? Or were our ancestors driven to create these monoliths in order to reconnect with celestial travelers who once walked the Earth? Could ancient monoliths hold advanced, extraterrestrial powers we have yet to realize? And if so, just what will happen when we unlock the mystery of the monoliths?

Giorgio Tsoukalos presents the fascinating story of Nikola Tesla, one of the most prolific inventors of the 20th century--and the man that actually electrified the world. Tesla is credited with shepherding mankind to a new industrial era and laying the groundwork for today's technological age. The genius inventor claimed he could visualize his inventions in full-detail and manipulate them in his mind. And he also claimed to have direct communication with intelligent beings on other planets. Is it possible that this alleged mad scientist, so far ahead of his time, was actually a human "receiver"? A being tapped to advance mankind--and pave the way for a future reunion with our alien ancestors?