Dark Places by Gillian Flynn meets All Good People Here by Ashley Flowers. 

I really enjoyed the character of Olivia. I admired her tenacity and her drive to support marginalized voices even when it seemed that the universe was punishing her for that choice. I also loved the character of Poppy. Even though her story is told mostly through flashbacks, her personality was very vivid. 

The plot was thrilling and went in some unexpected directions. I liked how Vincent's dementia was used to create a compelling reason for the unreliable narrator trope, and I liked the twist that

the manuscript was written with false information on purpose, as part of Vincent's final treasure hunt, to motivate Olivia to dig more deeply for the truth

. Everything tied together very neatly at the end, which elevated this book to one of my favorite thrillers. 

There were definitely some relationships that the book could have explored further, particularly Olivia's relationship with her partner Tom and with her former best friend Jack.