Su-il versus Su-il is a fantasy novel for children based on the text of an old Korean folktale, re-interpreted in the setting of modern Korean society. In the folktale, a lazy boy cuts his nails and throws them away carelessly. A rat happens to eat the nail clippings and turns into that boy. The rat, now the duplicate of the boy, kicks the real boy out of his home. Finally the boy gets the help of a cat to drive the rat from his home.In the novel, Su-il, the main character, is forced to take summer school by his parents whereas Su-il would rather play. Noting his unhappiness over this, his dog, Duk-sil, suggests to him that if he'd cut his nails and throw them outside, a rat would eat them and turn into his duplicate. He can then force the duplicate to take summer school while he plays and enjoys himself. Su-il follows this advice and it works! After sometime, however, Su-il realizes where he belongs and asks the duplicate to go away but he refuses. He eventually receives the help of a cat to drive the rat away and get his old life back. The author draws valuable lessons from the story in terms of parents-children relationships, self reliance, and the like.
Su-il follows his dog's advice and an old fable to create a duplicate of himself to go to school while he plays computer games and soccer, but when he is ready for things to return to normal, the other Su-il refuses to leave.