Six-year-old Lily Newman accompanies her mother, Charlotte, on a late-summer visit to her Aunt Beth's sheep farm in the middle of wild Welsh countryside. Beth, whom Charlotte considers to have greatly disappointed their parents by marrying a humble carpenter, now lives with her son and triplet daughters, her husband having died two years earlier.

While staying on the farm, Lily becomes fixated with a fairy tale her cousins make up about a Mushroom Man and vanishes one morning into the nearby forest. The adults suspect an abductor, while the children wonder if, indeed, their story about the Mushroom Man and his invisible-making powers has come true. As each group pursues their own solutions, relationships are strained and carefully constructed facades come crumbling down.

With sparkling prose, The Mushroom Man explores the fine border between reality and myth, and introduces Sophie Powell as a wry and sophisticated new talent in fiction.