The small cancer cell Kaja is tired of being the only one who cannot divide and make copies of herself. Especially now that the boss in the tumor has proclaimed they are going to spread and need all the divisions they can make. When even her best friend Moa manages to divide, Kaja has had enough, and sets out on a journey to find a way to mutate. Their journey through the body is fraught with danger, as it turns out that being a cancer cell on the loose is not so popular. And with each trial, Kaja questions if her plan to mutate is really that good. After discovering that she is part of a young boys body, she takes up the fight to save her world from ending.