A group of humans wage war against the rising evil of unidentified parasitic life-forms that live off of human hosts and strive to grow their power

Jung Soo In, who is infected with a parasite on her hand and start a strange cohabitation as it failed to steal her brain. Seol Kang Woo chases a parasitic water to find his missing sister, and Choi Jun Kyung is the team leader of the parasitic life team 'The Grey', and lives only to exterminate the parasitic water after losing her husband to the parasitic water.