Nine-year-old Max moves to Geroldseck Castle, together with his mother, who takes up a position as a geriatric nurse there. Apparently a shrewd thief is up to mischief here. His mother is suspected, she is threatened with dismissal. Therefore, together with the three residents of the old people's home at table no. 7, Max does everything possible to convict the real perpetrator.

Max can hardly believe his luck: In a retirement home, he has finally found a gang that will let him join! Admittedly, it's the oldest and most wrinkly gang in the world - but that doesn't matter. He's found the best friends a 10-year-old could wish for in the elderly Vera, Horst and Kilian. Especially when, like Max, you're bullied in your new class and need help. But the gang's attempt to improve his school situation backfires. Horst, a former Bundesliga soccer coach, challenges Max's over-ambitious gym teacher Stöhle to a soccer duel: the school team including Laura and Ole against a selection of old geezers plus Max! And then the castle is haunted and a new case begins...