Verity by Colleen Hoover

Lowen Ashleigh, a struggling writer, is hired to finish the remaining books of a successful series after its original author, Verity Crawford, is incapacitated in a tragic accident. Moving into the Crawford home to sort through research notes, Lowen discovers an unpublished, bone-chilling autobiography detailing horrific family secrets. As Lowen falls for Verity's grieving husband, Jeremy, she must discern whether the horrifying manuscript is a genuine confession or a dark writing exercise.