Bobby is a very bright but very sickly boy with a particular fondness for chess. As he starts fifth grade he is delighted to find that his teacher is the very popular Miss Gilden, with whom he forms a close friendship. Unfortunately, early in the school year, Bobby becomes too sick to go to school. After a short period of time, an alter-ego who looks exactly like Bobby appears and tells him not to worry, he will go to school for Bobby and come home and tell him what he has learned. Unfortunately, the alter ego terrorizes Miss Gilden, ultimately disgracing her and causing her death. As the alter-ego becomes stronger, Bobby becomes weaker until the alter-ego suggests that they play a game of chess to decide who should live as Bobby. With his life as the stakes, Bobby needs to best this evil version of himself. Assistance comes from an unexpected source.