Mathilde is actually pretty good in school, but the 13-year-old has a keen sense of justice that tends to trip her up. She is subject to fits of rage at the thought of environmental pollution, poverty and inequality, and they nearly get her expelled. The police don’t seem to do much to protect society’s weak, so Mathilde makes a snap decision to found her own detective agency. When she looks for potential staff, only two job applicants pitch up. Tobias is also 13 and spends most of his time alone on the computer or helping his father fiddle about with odd machines. The band of mini-Sherlocks is rounded out by Gustav, who would like to wow the world with his taekwondo skills, but hasn’t yet managed even a yellow belt. What he does bring to the table is the detectives’ first case. Gustav’s uncle is under threat from the henchman of a real, live gangster. The young gumshoes decide to investigate and the action begins.