Dolphin and her older sister, Star, live with their mother, Marigold, in a small London flat. Marigold, an avid lover of tattoos, suffers from bipolar disorder and also has a drinking problem. Dolphin loves Marigold and thinks she is wonderful and unique, while Star is embarrassed by Marigold's tattoos and erratic behaviour. Dolphin feels like an outsider at school; she is bullied by some classmates and feels her teacher is unkind to her. She also struggles with her dyslexia. Star appears to be more popular, and Dolphin dislikes the fact that Star has an older boyfriend. Dolphin later befriends Oliver, a shy and studious boy who spends the lunch period in the library to avoid being teased.
Marigold buys tickets to see her favourite band Emerald City, with the intention of finding Micky, Star's father, who Marigold still claims to love. Both girls are surprised when she returns that night with Micky. He was unaware he had a daughter and is thrilled to meet Star, and she adores him in turn. Dolphin dislikes him because she feels that he abandoned Marigold.
Micky sends both the girls presents, and Star goes to spend a weekend with him. Marigold hoped to reconcile romantically with Micky and is upset to hear that he has a girlfriend living with him. Micky hears of Marigold's behaviour and invites both Star and Dolphin to live with him. Dolphin stays loyal to Marigold and refuses to leave her so Star leaves to be with Micky. After Star leaves, Marigold has a mental breakdown and paints herself white using toxic paint. Dolphin has to phone her an ambulance and finds out that due to hermental illness she may be in hospital for some time.
With Marigold in hospital ill and tired, Oliver encourages Dolphin to contact her real father, who she knows nothing about, except that his name is also Micky and he worked as a swimming instructor. She manages to track him down and he's pleased to meet her. Dolphin hopes he will look after her, but he has a wife and daughters already and wants to do things properly, getting in touch with child services so Dolphin can be in foster care for a while. Dolphin is initially terrified of going into a foster home having heard Marigold's horror stories from her own childhood, but she stays with a kind older woman and several younger children and her father takes her to visit Marigold, who is on medication for bipolar disorder.
Star appears at the foster home after returning to the flat to find both Marigold and Dolphin gone. Star stays in foster care with Dolphin and although they argue at first, they reconcile and go to visit Marigold together. The story ends with Dolphin deciding that even though Marigold is in hospital and she and Star in foster care, they are still a family.