A Darker Shade of Magic by V.E. Schwab (2015)
Kell is one of two people in the world who can jump through the Londons. There’s Gray London, Red London, White London, and the untouchable Black London. Spread across the Londons are various degrees of magic leaving his home world of Red London with a pulse of magic in the air. Because of his power, he works for the kingdom of Red London, giving and receiving messages between the other kingdoms on their behalf. On his own time, he illegally transports items across worlds for individuals desperate for different tastes of magic. When a trade goes wrong, Kell ends up with a piece of powerful magic that could potentially change the balance 0f magic between the worlds forever. Even worse, in a robbery gone wrong, Lila, resident of Gray London, ends up with this very special piece of magic. Lila is hungry for an adventure and hopes that this magic can give it to her. Unwilling to let go of the magic, Kell must work with Lila to get the magic back where it came from before it lands in the w...