Maya's husband was killed.
Who killed Joe, her husband? Who killed her sister?
The whole book is about finding out the killer of her sister. Then more dead revealed.
The setup is pretty good as there isn't much loop holes.
The good friends are trying to help Maya as she seems to be losing her mind.
Maya is very determined.
The ending is a sad and surprising.
The relationship between Joe and Maya is the most mysterious. That's the key elements to this story. And good storytelling is like this, making you think of how relationship works. Characters should have dimensions, and this writer delivered.