The endless steppe has become crowded: mammoths are dying, Cro-Magnon tribes are fighting each other and, in between, exterminating the last Neanderthals. Semyon Vasiliev taught his tribe to store food, sculpt pottery, build boats and forge blades from meteorite iron. Will this be enough to survive and defeat his enemies? Again and again, Semyon stumbles upon traces of someone else's intervention. He already knows that representatives of a highly developed civilization have a plan for the accelerated development of humanity: the periglacial steppes should turn into almost a desert - tundra and forest-tundra, large mammals will disappear, and the surviving natives will be forced to take up farming. The creators of history did not take into account only one thing: a geologist who accidentally found himself in the Stone Age will love this world and will protect it.