A Darker Shade of Magic Novel by V. E. Schwab

A Darker Shade of Magic by V. E. Schwab is the first book in the Shades of Magic series, set in a world where multiple parallel Londons exist, each with varying degrees of magic. The story follows Kell, one of the last Antari, rare magicians with the ability to travel between these Londons: Red, Grey, White, and the long-lost Black London. Kell serves as an ambassador and smuggler, carrying messages between the realms. When he accidentally acquires a dangerous artifact from Black London, he becomes the target of powerful enemies.