Auntie Mabel and Pippin have been to stay with their friend Dora. But Pippin is frightened by Dora’s big dog and she leaves her little suitcase behind. When they get home, Auntie Mabel writes a letter to Dora. They take it to the Post Office and buy a stamp. Auntie Mabel decides to travel with the letter to see what happens to it. They watch letters being sorted, ride in a post van and on the night train. After a long journey they end up, with the letter, back at Dora’s.