The Devil’s Prayer by Luke Gracias

After the death of her mother, Denise Russo, Siobhan needs to understand what caused her to vanish six years earlier, and finds herself caught up in a nightmare centuries in the making.  Traveling to the convent in Zamora where her mother lived, Siobhan is in danger from the moment she arrives, and it is with great difficulty that she is able to access her mother’s final written confession. Reading it, she learns of a terrible betrayal that led her mother to make a deal with the Devil, risking Siobhan’s soul if Denise didn’t hold up her end of the bargain. As disturbing as all that is to Siobhan, other discoveries made in later parts of her mother’s confession are absolutely horrifying… as is the unfinished task her mother begs her to complete.