A boarding school without any storms, no adults, no rules: the best vacation EVER for the Einsteiners Io and Joyce. Until they are woken up in the middle of the night by strange noises after a film marathon. Were there burglars in the boarding school? A few hours later, while visiting their aunt Yagmur, the Pfefferkörner came across a new case in the nearby Erfurt monastery museum. Coincidence?

The peppercorns are looking for clues and signs of a break-in at the monastery museum, but Nesrin interrupts their investigative work. The Einsteiner is behaving very strangely. Something seems fishy here. Meanwhile, Io and Joyce are also looking for clues at the boarding school. Little do they know that the gangsters are closer to them than they think.

While Io and Joyce begin to secure the boarding school from possible gangsters, the Peppercorns secretly attach themselves to Nesrin's heels. But then another person appears out of nowhere. While Milan, Rafa and Lou slowly but surely get to the bottom of Nesrin's secret, the real danger is approaching from the forest.

The Peppercorns have fallen into Io and Joyce's trap. There's a lot of confusion. Now the peppercorns and the Einsteiners are faced with a decision: should they put all their cards on the table and continue investigating together, or can we not trust the others? While the gangsters are already hatching a plan to get rid of the children, an unexpected mobile home suddenly appears.

While Rafa and Nesrin search the forest for clues, Io and Lou explore the secret passage and make a surprising discovery. At boarding school, Paulina decides it's time to call the police. But before that happens, the gangsters, Leah and Tom, put a spanner in the works.

Crisis meeting at boarding school: Marlon and Paulina have been kidnapped and the gangster duo are demanding the treasure for their freedom. But our heroes don't give up that easily. While Nesrin and Rafa make a crucial discovery in the forest, the others at the boarding school begin to hatch a grand plan.