Apples Never Fall by Liane Moriarty

 Stan and Joy have been married for decades and have 4 now grown children. For years, they ran a popular tennis camp, but now they're retired and time is hanging heavy on their heads. Then one day, Joy disappears and Stan becomes the prime suspect. The kids are divided on whether or not Dad could have done something nefarious to Mom. And then there's Savannah, the mysterious young woman who showed up on their doorstep one night and who was invited to stay by Stan and Joy. Did she play a role in Joy's disappearance?

It's a twisty-turny plot that bounces between the past and the present as the cops try to figure out what really did happen to Joy. And what was Savannah up to? Couldn't put it down.