A stonemason Ajio, quiet, honest and conscientious by nature, works on road construction in Lailonia. One day, a hump grows on his back, which quickly turns into Ajio's double. Ajio's double is aggressive, vicious and lazy. He quickly manages to convince those around him that he is the real Ajio. Soon an epidemic of humpbacks affects all the residents of Lailonia. Real people are replaced by their doubles. They are aggressive and imperious. Ajio's double takes over the city of humpbacks. Only Ajio's son manages to escape the city. He hopes that when he grows up - he will return and deal with the humpbacks.