In the new school year, no one will call Daisy Wells and Hazel Wong small fry - after all, they are now in the eighth grade at Deepdean Girls' School. In honor of this great event, the friends decided to forget their stupid childhood fun and founded a secret detective agency. The first case - about the missing tape of classmate Lavinia - was so simple that it’s not worth mentioning (yes, yes, it’s not worth it, but there were no others at all). And the Wells and Wong Detective Agency would have shared the sad fate of the previously closed Pacifist Society and the Spiritualist Society, if Hazel had not accidentally discovered the corpse of the science teacher Miss Bell in the gym. And the friends decide to find the killer before the police. Because it's their business.