Autumn 1237. The Russian land froze in alarm: a huge horde of Batu was gathering in the steppe near the headwaters of the Voronezh River. Prince of Ryazan Yuri Ingvarevich is amassing forces on the border and sending messengers with requests for help to Vladimir and Chernigov. After all, if the help of neighbors does not arrive in time, the principalities of Ancient Rus' will be swept away one after another from the face of the earth: soldiers will die in a bloody battle, women and children will be taken into captivity, and cities and villages will turn to ashes. But one morning in the body of a young warrior Yegor Our contemporary, a history student and amateur reenactor, will wake up from border Yelets. With knowledge of the future, will he be able to change the course of history and prevent tragedy in the remaining weeks before the invasion? Or will he himself become one of the grains of sand that the Mongol horde will sweep away on its way?