Penny, Mark, and Marigold are made very unhappy in school because of a bully called Barry Hunter. Penny is fat; Mark wears thick glasses, is clumsy, and has a terrific temper. Both are made fun of only too easily. Marigold mixes with no one, rarely opens her mouth, and never smiles, and Barry calls her names. Then the angel arrives. She is blonde, beautiful, and shining clean, and all her clothes look new. The children are convinced she is a real angel, particularly when they find her name is Celeste. Celeste takes on Barry with a vengeance, and soon she is keeping a written record of all Barry's bullyings, which the other children sign as witnesses. Mr Fairweather, their teacher, who has managed to turn a blind eye to all that has been going on (he thinks children should work these things out for themselves), must finally admit the pain and humiliation suffered. Celeste is leaving the school (was she really the recording angel that Marigold has told them about?) and leaving behind Penny, who is thinner, Mark, who is learning to cope, and Marigold, who has begun talking to the other children. She is a unique and lovable heroine, whoever she is.