Kez is a traveller girl, living with her mum in an old Bedford bus, enjoying life on the open road. Then one day disaster strikes - Kez's mum goes missing, the police raid the site, and before she knows it, Kez has been whisked away into a foster home. Her new foster mother has been taking in children for many years, and in fact Kez is the 99th - and so becomes known as Number 99. With the help of the first foster child - Number 1, now a high-up civil servant - Kez sets out to find what has become of her mother. However, they find their way barred at every turn, and soon realize there is a high-level conspiracy to stop them finding her. Eventually they discover that Kez's mum had identified an illegal genetically-modified crop of wheat near the site where they lived, and has been spirited away to stop her revealing her knowledge before the crop is safely harvested. The race to find her is fraught with obstacles and danger, but Kez has a fighting spirit.