The main content of The Adventure of Onion is the struggle of the poor such as Onion against the ruling class of the rich such as King Lemon.

The story begins with the old onion accidentally stepping on the corns of King Lemon and being arrested and sentenced to life imprisonment. From this, the onion knows the injustice in the world and is determined to travel around the world, learn how to live and save all the good people in prison. Later, when he came to a village, he saw the tomato knight ruthlessly take away the small house that Grandpa Pumpkin had worked so hard to build all his life and decided to fight back. He United more and more poor people, and after many tortuous struggles, he finally drove the rich out of the castle. The flag of freedom was raised above the castle, and the castle became a children's palace. Explorers have to be self-reliant and take part in labor; The poor became masters.