In which the Moomin characters are in fact tiny creatures living secretly in a normal human countryside, however the main characters (perhaps the main cast of Finn Family Moomintroll [Moomintroll, Snufkin, Sniff, Snorkmaiden, Snork, Mr. Hemulen, Moominpappa, Moominmamma, maybe throw in Little My if you so desire] give or take) get lost from their secret small creature society that resembles the regular canon and end up at the cottage of a normal human girl named Alicia who lives with her grandma Clarissa.
Alicia is a neglected young girl who finds these creatures and takes an adoration to them, making friends with and helping them in various ways and in return the small creatures help her aswell with things such as homework. Alicia is hesitant to reveal these creatures to her grandma for various possible reasons that could be unfounded. Later it's revealed that Alicia, her grandma and other humans in the settlement are in danger of being kicked out of their land because Corporations™.
The day is saved thanks to the small creatures sneakily scaring off the people running the corporation and there's a big celebration at the end.
Optional: All the while, there's been a search party for the Moomin family. Eventually they find them and perhaps help in the story's climax against the bad guys and after all is said and done they have to go home, there's an emotional goodbye between Alicia and the family and each go their separate ways, never forgetting the memories they've made.