I'm not from here. Book one. Cry baby

The era of the Moscow Tsar Ivan the Third Vasilyevich (the fifteenth century) represents a turning point in the history of Russia, namely, the deliverance of Russia from the Tatar-Mongol yoke, at this time our contemporary also falls, but he falls as a baby, being fifty years old in our time. Why and how it happened, and how an adult can feel himself, being a baby, but retaining his consciousness, and even five hundred years ago...