WHAT A GOOD THREAD I hope you don't mind me popping here every once in a while!
This is actually a thing I'm writing in a detail for nano, but Rosemarie, her friend Karl and Karl's brother Thomas get into quite an adventure when Rosemarie gets a new classmate called Ilja. She is super determined to make friends with the weird boy, but Ilja soon turns out to be a rather hard one to crack: he doesn't speak to others, spends all his time alone and in generally denies each and every single friendship offering he gets, and this only makes Rosemarie even MORE determined to become his friend & learn why he is like that, because it's definitely strange. When Rosemarie ends up witnessing the way Ilja lives she is only more curious: he lives on what the kids call "the green district" which is kind of like this bohemian artist area with a lot of plants around, gaining its nickname, and there he seems to live not with his parents but some man who looks similar enough to be his relative, but too young to be a father.
Through more misadventures Rosemarie and Karl end up witnessing Ilja being chased after two adult men, and as an act of self defense Ilja cuts part of one of the men's ear and together with that + Karl and Rosemarie appearing on the scene the men are forced to leave before they attract the attention of other people. There Ilja explains them the men have been after him since he moved here form his home country, and they want the key Ilja keeps as a pendant around his neck: it was given by his parents who were publicly executed for possessing illegal books, and the key would open a locker inside the local library with supposedly a book inside the men want. Ilja himself doesn't know anything about it, but knows it's really important and that his parents bestowed the key to him because they were desperate and knew they would be caught soon.
Rosemarie then crafts up a plan to help Ilja: as Rosemarie is fast and knows the streets like her own pockets, she and Ilja switch clothes and Rosemarie pretends to be Ilja to distract the men while Ilja and Karl go get the book from the library. Somehow they manage to succeed and find out the book is written in a language none of the kids can read, and that it's full of notes in Ilja's language, done most likely by his parents. They don't know what to do with it, but they decide to go to the used book store the next day, buy a book that looks seemingly similar in covers and together with the help of Thomas, Karl's sickly but very smart brother they manage to make the fake book look like it's full of secret codes and cryptic notes, and they put that book inside the library's locker instead.
The next time the men are chasing after Ilja, Ilja pretends to put up a fight but eventually gives up his key to the men, pretending it's his last chance. The men take it and end up taking the fake book from the library and return to their own country, convinced it's a code to be cracked. It's safe to say even the men weren't exactly sure what the book contained since it was Ilja's parents who used it for whatever their purpose was. Then, at least for the time being, Ilja is free now and doesn't need to fear the men are going to get him anytime soon.
HONESTLY all the adventures of these kids are inspired by those wacky youth literature adventure stories I read as a kid and I'm really trying to convey the larger-than-life sense of adventure there with ridiculous plots haha