Shinichi sets out for revenge and runs into an unexpected ally. Together they team up to take down the Parasyte that brutally attacked Shinichi's family. But when Migi falls asleep, Shinichi is forced to engage the enemy on his own.

The divide between Shinichi and Satomi continues to grow. Shinichi's classmate, Yuko, investigates Hideo and unknowingly stumbles upon a dangerous secret. Meanwhile, Ryoko Tamiya, now known as Reiko Tamura, plots behind the scenes.