Evil Within by Winslow Swan

The Tanner's are not your ordinary family. April is a successful author, her husband John a scientist and their son Bobby at ten years old is quickly becoming a child prodigy in the world of art. They have just moved into their dream home where they plan to spend the rest of their lives. That dream quickly becomes a nightmare as a talisman in the form of a small stone has invaded their peaceful lives and brought out the Evil Within. From the writer of "The Convincer" and "The Jake Rhodes Mysteries" comes a tale of murder and sexual depravity that brings an extraordinary family to the very edge of madness.