A Darker Shade of Magic (V. E. Schwab)

The story started slow: it wasn't until nearly 1/3 of the way through that the two main characters met and the main problem was engaged. Until then there was a lot of world-building, with parallel London joined by magical doors only a select few can cross. There was also a rather stereotypical Feisty Female character, fun but a bit one-dimensional. By the middle, though, the action, and my interest, picked up, and it was satisfying enough in the end.