There's a lot here to like - Zevin is a master storyteller, in that she can give a pencil sketch of a person the appropriate characterizations in a few strokes of her pen. She also creates suspense without any of the normal mystery writer tropes. It's a superb talent, and it's why I liked The Storied Life of A.J. Fikry so much, and why I will continue to read her stuff.
What fell flat was the final chapter. Up until that point, you understand Aviva from afar - or you understand and empathize and are proud of her for pulling herself up by her bootstraps. But, that final chapter had a decent number of what I will call "character holes", such that by the end of it I was far less enamored with her. Her choices seemed odder than I expected, and her revival in Maine seemed inconceivable in the way that Zevin described it.
However, I did dearly love Ruby. (Who doesn't love a precocious 13-year-old... on paper?) Her pen pal letters were at times even laugh-out-loud funny. And I appreciated the chapter with Embeth because she was such a confusing, yet appealing character - exactly what I would have expected from the jilted party.