A Gathering of Shadows by V.E. Schwab
Synopsis from GoodReads:
Four months have passed since the shadow stone fell into Kell’s possession. Four months since his path crossed with Delilah Bard. Four months since Rhy was wounded and the Dane twins fell, and the stone was cast with Holland’s dying body through the rift, and into Black London.
In many ways, things have almost returned to normal, though Rhy is more sober, and Kell is now plagued by his guilt. Restless, and having given up smuggling, Kell is visited by dreams of ominous magical events, waking only to think of Lila, who disappeared from the docks like she always meant to do. As Red London finalizes preparations for the Element Games—an extravagant international competition of magic, meant to entertain and keep healthy the ties between neighboring countries—a certain pirate ship draws closer, carrying old friends back into port.
But while Red London is caught up in the pageantry and thrills of the Games, another London is coming back to life, and those who were thought to be forever gone have returned. After all, a shadow that was gone in the night reappears in the morning, and so it seems Black London has risen again—meaning that another London must fall.
A Darker Shade of Magic by V.E. Schwab
Synopsis from GoodReads:
Kell is one of the last Travelers—rare magicians who choose a parallel universe to visit.
Grey London is dirty, boring, lacks magic, ruled by mad King George. Red London is where life and magic are revered, and the Maresh Dynasty presides over a flourishing empire. White London is ruled by whoever has murdered their way to the throne. People fight to control magic, and the magic fights back, draining the city to its very bones. Once there was Black London—but no one speaks of that now.
Officially, Kell is the Red Traveler, personal ambassador and adopted Prince of Red London, carrying the monthly correspondences between royals of each London. Unofficially, Kell smuggles for those willing to pay for even a glimpse of a world they’ll never see. This dangerous hobby sets him up for accidental treason. Fleeing into Grey London, Kell runs afoul of Delilah Bard, a cut-purse with lofty aspirations. She robs him, saves him from a dangerous enemy, then forces him to another world for her ‘proper adventure’.
But perilous magic is afoot, and treachery lurks at every turn. To save all of the worlds, Kell and Lila will first need to stay alive—trickier than they hoped.