What almost ruins the family's trip to Paris and what do they think might be the reason?

After riding on the train for a while, Anna sees a sign for Stuttgart and realizes that the porter has put them on a train to Germany. If they end up in Germany, Papa will be carried off by the Nazis. When Anna tells Papa, he has them stop the train before Stuttgart. Max gets their things and they get on a train for France. They wonder whether the porter had been trying to get the one-thousand Mark reward for Papa.