The Sorcerer - Victor Pylaev

Was he a hero, a warrior, a savior, a defender of the helpless? A knight without fear or reproach?
No, nothing like that. Even among the gifted, he was known as a sorcerer, a warlock, a shapeshifter—one with a reputation firmly rooted in the darker side. But even such a man wouldn't turn his back on an old friend in need, especially not when the world seemed on the brink of collapse.
If only he had known the consequences his meddling would bring!
His genius didn't help him, and his unique ritual sent him farther into the past than intended. Worse still, it cast him into an alternate history—the year 1909 in the Russian Empire. This strange new world is ruled by aristats with powerful magical talents, and all manner of evil spirits, ghouls, and monsters crawl out of Breaches in reality, spilling into the streets of St. Petersburg. Now, with no friends, no allies, no money, and no title, he's stuck in the body of a skinny teenage boy. To survive, he must regain his former abilities, learn new ones, and find a way back home. But for him, this is just a minor setback.
His mission is far from over. He still has a job to do: save his world.