1957, south-east suburbs of London.
Jean Swinney is a feature writer on a local paper, disappointed in love and - on the brink of forty - living a limited existence with her truculent mother.
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 she investigates, the more her life becomes strangely (and not unpleasantly) intertwined with that of the Tilburys: Gretchen herself, her husband Howard - with his dry wit and gentle disposition - and her charming daughter Margaret.
But they are the subject of the story Jean is researching for the newspaper, a story that increasingly seems to be causing dark ripples across all their lives. And yet Jean cannot bring herself to discard the chance of finally having a taste of happiness.
But there will be a price to pay - and it will be unbearable.