Books like The Wizard Hunters

Those who read The Death of the Necromancer (related to this book, but not requisite for understanding it) will remember Vien as an urbane, prosperous city at the height of its power. From a cultural capital and political powerhouse, it has transformed in the space of only a few years as a mysterious and apparently unstoppable enemy reduces the city to ruins and its inhabitants to refugees. Before the war, Tremaine was a successful playwright with a circle of entertaining arty friends. Now she volunteers for the dangerous work of driving ambulances and goes home alone to her missing father's rambling old house of Coldcourt. To help the dismal war effort, her family has donated both money and their collection of magical spheres to a research group trying to find a way to circumvent the enemy's immunity to magic. One night one of the wizard researchers, a family friend, comes to ask Tremaine if she has any additional spheres. Little does she know that her decision to accompany Gerard to the Institute will send her into danger and across dimensions...