Fool Me Once by Harlan Coben

Maya is back home with her husband Joe and baby Lily after an incident in Iraq ended her military career. She's still mourning the death of her sister Claire, who was murdered while Maya was still overseas. Then she and Joe get mugged in the park one night and he too ends up dead. And most puzzling is that the police tell Maya that the same gun killed Joe and Claire.

One night, Maya is reviewing the footage from her nannycam when she suddenly spots Joe, playing with Lily. But how can that be? Is she losing her mind or is someone messing with her mind?

Fool Me Once is quite the page-turner and there are a couple of really good twists at the end.
It would be a great choice for a long plane ride this summer vacation season.