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!