By the Pricking of My Thumbs. Tommy and Tuppence Mystery #4 - Agatha Christie

By the Pricking of My Thumbs is the 4th book in the Tommy and Tuppence Mystery Series. An old woman in a nursing home speaks of a child buried behind the fireplace... When Tommy and Tuppence visited an elderly aunt in her gothic nursing home, they thought nothing of her mistrust of the doctors; after all, Ada was a very difficult old lady. But when Mrs. Lockett mentioned a poisoned mushroom stew and Mrs. Lancaster talked about "something behind the fireplace", Tommy and Tuppence found themselves caught up in an unexpected adventure involving possible black magic...