Alva and Irva Dapps are identical twin sisters. They live in the city of Entralla, not a place you are likely to have visited. Alva is by nature an explorer; she longs to travel the world. Irva is a recluse, for whom a step outside the house is an ordeal. But the twins belong together -- they feel each other’s feelings, think each other’s thoughts, suffer together, love together and hate together -- they cannot survive without each other. Since childhood, the twins have built fantastical cities of Plasticine. But when Irva finally refuses to leave the house at all, the major work of their lives begins. Alva, attempting to return Irva to life, brings the city of Entralla into their home; she wanders its streets, observing, taking notes, measuring, and reports her findings to Irva, who painstakingly constructs a miniature Entralla of Plasticine. And the model city comes to serve Entralla in a way its creators could never have imagined.