Deadly Assignment by John W. Daniel

When a letter arrives at a small North Carolina newspaper from a man claiming a connection between his missing daughter and the recent murder of another young woman, life gets even more complicated for feature writer Abby Burlew, a recovering drug addict who has bipolar disorder. Since no one else at the paper is available for the assignment, the editor reluctantly sends Abby to a remote barrier island to investigate. What seems like an open-and-shut case quickly turns into a tangle of mysterious goings-on, hidden motives, and unlikely suspects. Abby’s problems are compounded when she becomes romantically involved with the island’s chief deputy, despite mounting evidence that he’s a womanizer and a suspect himself. Her sanity—and ultimately her life—are now at risk as she pursues this increasingly stressful and dangerous assignment.