Darker shade of magic

A Darker Shade of Magic, from #1 New York Times bestselling author V.E. Schwab
Kell is one of the last Antari—magicians with a rare, coveted ability to travel between parallel Londons; Red, Grey, White, and, once upon a time, Black.
Kell was raised in Arnes—Red London—and officially serves the Maresh Empire as an ambassador, traveling between the frequent bloody regime changes in