Emil and the Detectives (Red Fox Classics)

Kästner wrote this in 1929. It has subsequently been made into several movies (including Disney) and translated into over 50 languages. Young Emil Tischbein, our protagonist, is sent to Berlin to visit his grandmother. He is also given some money to pass on to her. Emil pinned the envelope with the money to the inside of his jacket to keep it safe.

On the train, Emil meets a man named Herr Grundeis who gives him a chocolate bar to eat. After eating it, Emil falls asleep. When he wakes up, his envelope with the money is gone and so is Herr Grundeis. Luck is with Emil however because he spots Herr Grundeis in Berlin. Emil runs into some local kids (who call themselves "the detectives") who decide to help him and the adventure is underway!