Hraï, Oko and Tour come across extraterrestrials in search of oil to repair their saucer and be able to return home. Together, they cross Europe, find themselves defending Bulgaria invaded by enemies, discover an aqueduct in Italy and narrowly escape the Inquisition in Spain.

The Cossacks become involved in a dispute between the gods Zeus and Mars. Zeus wants to set up the Olympic games, while Mars wants to undermine him and start more wars. The Kozaks help Zeus and challenge Mars at the Games.