A Gathering of Shadows | V. E. Schwab

Kell is one of the last magicians with the ability to travel between parallel universes, linked by the magical city of London. It has been four months since a mysterious obsidian stone fell into his possession and he met Delilah Bard. Four months since the Dane twins of White London fell, and the stone was cast with Hollands dying body back into Black London. Now Kell is visited by dreams of ominous magical events, waking only to think of Lila. And as Red London prepares for the Element Games an international competition of magic a certain pirate ship draws closer. But another London is coming back to life. The balance of magic is perilous, and for one city to flourish, another must fall...