Peter Bell the Third, accidentally named from the title of a poem by Percy Bysshe Shelley, is called upon to renew his old friendship with Rowland Usher, who was deliberately named after the protagonist of a story by Edgar Allan Poe. In the new House of Usher that Rowland is growing in the Orinoco Delta, Usher explains the scientific work in genetics that he's doing there to Peter, while they both mourn Rowland's dead twin sister, Magdalen, who has apparently committed suicide for reasons that no one quite understands. As a scientist, Peter is inevitably convinced, when he discovers Magdalen's "ghost" haunting the house, that the haunting can only be figurative and symbolic—but that does not make it any less meaningful, or problematic. A marvelous new novel in this long-running series by a master of biological extrapolation.