In the spring of 1223 from the birth of Christ, hordes of unknown warriors appeared on the southern borders of Rus'. These were the brave Mongols who had already conquered half the world. But no one in the Russian lands had ever heard of them and did not know what to expect from these steppe inhabitants. Pursuing their enemies the Polovtsians, who by chance turned out to be relatives of the Russian princes, the Mongols approached the very borders of the Russian state. But at this very time and to this very place, by the will of fate, the innovative mechanic Grigory Zabubenny was transported from the twenty-first century. And he found himself in the thick of things, becoming a participant in the fateful meeting of the Mongols and Russians on the Kalka River. What will happen next? How will the battle on Kalka go now? Where will the Mongols turn after this? And... where will Rus' turn?