The whole world is about to change one quiet evening with the arrival of parasytes who devour human brains. One of their eggs lands at the home of Izumi Shinichi, a high school student. The hatched parasyte attacks Shinichi, but it faces unexpected resistance and fails to infiltrate his brain.

As the number of mincemeat murder victims grows, Shinichi, alone in his knowledge of the truth, is in turmoil. When Migi suddenly alerts him to the presence of another parasyte, he is aghast to find that it is in his own school. Paranoid, Shinichi attends a schoolwide assembly, where the staff introduce a beautiful new teacher...