Invaders. Book 1. The Secret of the Mouse King

Theodore, who everyone simply calls Teddy, turned thirteen, and everything around her changed. Her perpetually busy father, who used to show care and love through gifts and fulfilling all her whims, suddenly cooled off and found a new wife, bringing not only a stepmother but also her son into their home with Teddy. Fortunately, the stepmother turns out to be nothing like Teddy imagined, and her stepbrother Dimka becomes not only the life of the party at school but also his sister's best friend. But this is just the beginning, as their father sends both of them to spend the entire summer with their grandmother in the village. Jumping off the train at a station that wasn't on the schedule, the teenagers don't even suspect that they will end up in a parallel world where mice and birds are the size of humans, and people seem to have found themselves in a mysterious valley straight from the 16th century...