The Winter Sister by Megan Collins 

Sixteen years ago, Sylvie’s sister Persephone never came home. Out too late with the boyfriend she was forbidden to see, Persephone was missing for three days before her body was found—and years later, her murder remains unsolved.

In the present day, Sylvie returns home to care for her estranged mother, Annie, as she undergoes treatment for cancer. Prone to unexplained “Dark Days” even before Persephone’s death, Annie’s once-close… Read more.