Little Merry Murder by Cheryl Bradshaw

As Claire Cooperson sits by the fire, wrapping presents and putting them beneath the Christmas tree, she hears what sounds like glass shattering. The unwelcome noise startles her, and she jumps up, tiptoeing toward the back door. A chill brushes across her face, and as the outside wind howls, she wraps her arms around herself, pulling her sweater tighter.
Struggling to see in the darkness, Claire switches on the dining room light and finds the cause of the sound she heard. A glass panel in the center of the back door has shattered, spitting jagged shards all over the tile floor.

But what caused the glass to break?
And why does Claire have a sinking feeling—a feeling telling her she’s no longer alone?