Oona, the 13 year old sleuth of this YA fantasy/mystery, lives on Dark Street, a one street town lying between the New York of 1876 and the land of the Fay. Every midnight for one minute there's an open gate between NYC and Dark Street, and the rest of the time the city is inaccessible. Oona was apprenticed to her uncle, the Wizard of Dark Street, their only wizard, and the person who protects the town against possible fairy attack. Three years before the book starts, she accidentally killed her family with a spell gone wrong and now she doesn't trust magic. She's grieving and guilty, so she's lost heart and decided to give up her apprenticeship and open a detective agency. The Wizard has begun to interview apprentice candidates when a magical floating dagger stabs him, leaving his clothes on the ground and the Wizard vanished. It transpires that the dagger may not have killed the Wizard, so Oona goes in search of her uncle and the person who committed the crime.

It's always nice to read about intelligent people doing clever and brave things, and that recipe seems to work particularly well in YA. This book shares DNA with a lot of YA fantasy and detective novels, particularly The Mysterious Benedict Society books, Agatha Christy, and Edward Eager. Aside from those resemblances, I thought the author did a great job of making Oona sound like a real person with a personal history, right from the start. In most YA we're introduced to the protagonists as nearly blank slates (usually to give the author room to let them grow). Oona certainly grows, but she isn't presented to the reader as a blank. She's grieving, and this is the emotional setup for the story. If you compare to, say, Harry Potter, Harry has a backstory but he is presented as being in a sort of equilibrium when the story starts and events just happen to him because he has no agency. That is what's usual for fantasy novels. Oona's in the process of making dramatic life changes that are under her control, then she's thrown for a further loop and must respond. That's what makes this book different and worth reading.