Everywhere That Mary Went by Lisa Scottoline

Mary has been slaving away for the past eight years trying to make partner in her cutthroat Philadelphia law firm. She's too busy to worry about the crank phone calls that she's been getting-until they fall into a sinister pattern. The phone rings as soon as she gets to work, then as soon as she gets home. Mary can't shake the sensation that someone is watching her, following her every move. The shadowboxing turns deadly when her worst fears are realized, and she has to fight for something a lot more important than partnership -- her life.