1957, south-east suburbs of London. Jean Swinney is a feature writer on a local paper, disappointed in love and - on the brink of 40 - living a limited existence with her truculent mother: a small life from which there is no likelihood of escape. When a young Swiss woman, Gretchen Tilbury, contacts the paper to claim that her daughter is the result of a virgin birth, it is down to Jean to discover whether she is a miracle or a fraud. But the more Jean investigates, the more her life becomes strangely (and not unpleasantly) intertwined with that of the Tilburys: Gretchen is now a friend, and her quirky and charming daughter Margaret a sort of surrogate child. And Jean doesn't mean to fall in love with Gretchen's husband, Howard, but Howard surprises her with his dry wit, his intelligence and his kindness - and when she does fall, she falls hard.