So the summary is a total misdirect because the story isn't about the money and who gets it at all. It's really about why. And, yeah, there are dark family secrets, but this isn't a thriller. There is very little sense of danger or suspense. More curiosity. Though curiosity will carry you a long way.
The writing also isn't engaging for me. Barnes came up with an unfathomable number of cliches to describe the first act as surreal. We get it. But despite the host of semi-interesting characters, I didn't feel much of anything throughout the story. Not suspense or anticipation or excitement or revulsion. It's simply not an emotionally engaging story.
Admittedly, I was trying to pay too much attention looking for clues, like looking for the trick at a magic show. If it were an intellectually engaging book then that would have balanced the lack of emotion. But it's not much of that either. The secrets are so insular to the fictional world, the reader can't really engage with them the way you would in a mystery novel. You're kind of along for the ride as the characters make discoveries. There's so much more potential in a book about a living riddle and a house with secret passages, but I didn't think it really lived up to that potential.
The thing that REALLY bothered me, though, was how repetitive Barnes is. I would chalk it up to going for bestseller status so feeling the need to make sure the lowest common denominator is engaged. But if any character said something significant, you can be sure it would be repeated no less than 6 times later in the book. The same statements again and again and again kind of drove me crazy.
Also, because I was paying so much attention to clues, I think I found an editorial error. (show spoiler)[Right after Avery reads the Red Will and figures out the boys' middle names are clues Jameson says his grandfather picked all their middle names except Nash. But that never comes into play later in the story. It isn't a key in the mystery. Skye just got done saying she didn't pick her sons' middle names and Nash is her son and I didn't see anywhere else that he was excluded from that statement so the best I can figure in earlier versions of the story Tobias didn't choose Nash's middle name, Jameson said that and when the story changed it didn't get updated.] It really bothered me for several chapters though, because I noticed the anomaly and kept looking for the moment it was something more than an error.
The boys really are the engaging part of the book that makes it work, their Saturday games, their different perspectives, Xander is funny and adorable. The more Avery interacts with them, even more than interacting with the mystery, the more interesting the story is. Though, a little like the house with all the secrets, the boys had potential to be even more interesting.
I think part of why it isn't engaging is because everything happens so fast and feels like it has no impact. (show spoiler)[Avery gets shot. Then she's going shopping. Wait, it was Drake. Libby is at the police station. Libby is home. Avery trashed her phone. Now she's at a gala.] There is never time to slow down and DWELL for a moment. I wish things would have simmered, at least the important things so they could hit better.
And if I had read it simply for fun and not to try to solve the puzzle, it would have been just lighthearted fun and the flaws woudn't have been that big of a deal.