Here is a synopsis from the author's website:
Ghosts, a kidnapping, a crew of young detectives, and family secrets mix in this new standalone mystery set in the world of the bestselling Greenglass House, from a National Book Award nominee and Edgar Award-winning author.
Marzana and her best friend are bored. Even though they live in a notorious city where normal rules do not apply, nothing interesting ever happens to them. Nothing, that is, until Marzana’s parents are recruited to help solve an odd crime, and she realizes that this could be the excitement she’s been waiting for. She assembles a group of kid detectives with special skills—including the ghost of a ship captain’s daughter—and together, they explore hidden passageways, navigate architecture that changes overnight, and try to unravel the puzzle of who the kidnappers are—and where they’re hiding. But will they beat the deadline for a ransom that’s impossible to pay?
Legendary smugglers, suspicious teachers, and some scary bad guys are just a few of the adults the crew must circumvent while discovering hidden truths about their families and themselves in this smart, richly imagined tale.
Okay, first, if you haven't read Greenglass House, you're gonna want to take a break and read it immediately. It's one of the best books I've read. I picked it up at the Scholastic Book Fair at my last US school after a student told me it was one of her favorites, and I devoured it in like three hours. The world of Greenglass House is probably my ideal fiction world: a coastal town (non-specific North Atlantic in this case, although I would also accept Cornwall) with intrigue, old buildings, smugglers, adventure, etc. While I don't think I could participate in any dubiously legal shenanigans myself, I would love to own a cafe or bookstore in such a town. I would absolutely have a hidden room or passage behind a bookcase.
Anyway, I don't want to give away any of the plot twists because the books in the series are mysteries. But I will say that the world-building is exquisite. I cannot overstate how much I love the vibes of this book. I'm a little sad it took me so long to get into the headspace to read it (I've had it since it came out), but this week I've had literally no work to do but have been required to come in to finish my contract, so yesterday, my friend and coworker Taty and I had a reading party -- we brought snacks and read for the whole day.
This book is technically the fourth book in the series, but it is also a standalone mystery. The references to the previous books deepen the flavor, but it's been six years since I read the first book, so I didn't remember a lot of the things that happened, and I didn't feel like I missed anything important while reading this book. If you pick up the series, you should definitely read Greenglass House and then Ghosts of Greenglass House first and second because Ghosts builds on the first book. Bluecrowne and The Left-Handed Fate are sort of prequels as they are set in the 1800's, I think.
Anyway, these books are absolutely delightful and you should read them.