Season 1

After a brutal attack, Jeong Su-in learns she may not be the same person as before. Choi Jun-kyung discovers the monsters are forming an organization.

Looking for his sister, Seol Kang-woo investigates Saejin Church, where he finds Su-in. But he soon encounters trouble — and the two fight to escape.

After raiding Saejin Church, Jun-kyung begins suspecting Kim Chul-min is hiding something — later tracking him down meeting with Su-in and Kang-woo.

After revealing everything he knows to Chul-min, Kang-woo agrees to help save Su-in. But when the plan goes awry, lives are put at risk.

Despite being on the run, Su-in tries to warn Jun-kyung. But as Team Grey's raid plays out, Su-in and Kang-woo realize it's all part of a bigger plan.

Su-in meets with Seol Kyung-hee, who requests an alliance. But the parasites' ploy for power goes into full effect — and it's up to Heidi to stop them.