Martin sits thoughtfully in the kitchen with his aunt, who had cancer, and asks her what cancer exactly is. She then tells him the story of the "cellings" in the human body. Slowly, some cellings turn into "cancerlings," because they are angry about the "rubbish" in the human body resulting from wrong nutrition or air pollution we breathe in. They are spreading and threatening the cellings. A fight breaks out. Will they manage to defeat the cancerlings in the end? In her book, Marion Hartmann describes the development and treatment of cancer from inside the human body. The cells become living beings and thus identification carriers with which children can better understand the disease cancer. As a person affected, she hopes to make it easier for children to understand and for parents to talk about the disease.