The Slanted Worlds (Obsidian Mirror Series #2)

Part Dr. Who, part Blade Runner, and part A Midsummer Night’s Dream, a genre-busting fantasy from the author of Incarceron
 
In book two of the critically acclaimed Obsidian Mirror series, New York Times bestselling author Catherine Fisher, called “the first lady of British fantasy” by the London Times, once again shows us that she is a master of world-building and surprising plot-twists. Jake, Sarah, and Oberon Venn continue their fight for control of the Obsidian Mirror, and whoever wins will either save a life, change the past, or rescue the future.
But the Mirror has plans of its own.