Beneath the Stairs by Jennifer Fawcett

Few in sleepy Sumner’s Mills have stumbled across the Octagon House hidden deep in the woods. Even fewer are brave enough to trespass. A man had killed his wife and two young daughters there, a shocking, gruesome crime that the sleepy upstate New York town tried to bury. One summer night, an emboldened fourteen-year-old Clare and her best friend, Abby, ventured into the Octagon House. Clare came out, but a piece of Abby never did.

Twenty years later, Clare receives word that Abby has attempted suicide at the Octagon House and now lies in a coma. With little to lose, Clare returns to her roots to uncover the darkness responsible for ruining their lives.