Book — Riley Sager

Something is lurking beneath the water's surface...
Recently widowed actress Casey Fletcher has escaped to her family's lake house for peace and quiet. She's been happily losing herself in her thoughts and several bottles of bourbon, until the glamorous couple across the lake catch her attention. They look so perfect - just like Casey and her husband used to be.
But is anyone what they seem?
Casey has a detective sat at her kitchen table.
She has a man bound and gagged upstairs.