Hi! I hope you can help me because this is driving me batty LOL. I believe it was a book or series of children’s books. There was some sort of isolated world outside time, but it was starting to show cracks and it was feared their world was ending. Two children believed a girl on a train being sent away from London during the war was responsible, so they traveled in time and kidnapped her . Ultimately, they were convinced she was innocent. Then, they had to hide her as a visiting cousin; there was a lot of advanced technology, like a money chip and a pen that had special abilities when she went to school with them. The place traded with other time eras; there was a river around it that played into the plot. Ultimately, I believe an uncle and his daughter were the bad guys. There was a battle; the children were locked up in some sort of phasing clock tower. There was a powerful, godlike couple who ultimately woke up/remembered their real selves and put everything to rights. I believe the girl’s family was saved and allowed to come live with her there. That’s all I can remember. Thanks very much!