With Shinichi at the brink of death, Migi takes drastic actions to ensure his host's survival. After a trying recovery, Shinichi learns that his father is still alive and races to his side before the Parasyte that attacked his mother strikes again.

Life has returned to normal, but Shinichi has not as his ties to Migi continue to change him. As those around him grow wary of this 'new' Shinichi, a Parasyte named Hideo Shimada emerges from the shadows and begins attending Shinichi's school.