The Red Planet, the closest to us and the most mysterious. She always attracted and frightened. She excited minds, threw up riddles. And then the centuries-old dreams of earthlings came true. The astronauts landed on the shore of an ancient dry ocean, where amazing structures suspiciously similar to artificial formations were found in the last century: Dome, Pyramid, City, Face. Ancient Babylon and Egyptian pyramids, dead cities in different parts of the Earth - Teotihuacan and Hara- Khoto... Not only are they somehow connected with the famous Martian Sphinx. He inhospitably meets a top-secret expedition whose task is to deliver to Earth gold discovered by automatic stations on the Sidonia Plain...