Giorgio Tsoukalos contemplates whether aliens that once visited Earth deliberately left a series of clues that mankind was eventually meant to decipher. Many ancient sites, and even recent ones like Roswell, all seem to be associated with reports of something coming down from the sky. Tsoukalos' research demonstrates that many of these places share a common symbol or shape-concentric circles. What is the significance of these designs, and is it possible they contain a coded message left by alien visitors?