Emily and Alexander visit their cousin Gaston. He is a passionate flyer and takes part in the first race from London to Paris, which is held for mice and rats in parallel with the human race. Gaston is friends with a human child, Carole, who also participates in the race with her father. Louis, her father, hires a pilot, Reginald, because he thinks he has a better chance of winning. But a millionaire from America hires him and sabotages the planes of the other participants. There is also a saboteur in the mice and rats camp, whom Emily and Alexander know from before.