Colony plot recap, spoiler-light
Scientist Seo Young-chul triggers a bio-terrorist nightmare at a Chains Bio conference in the Dongwoo-ri Building after accusing CEO Kang Woo-chul of research plagiarism. Injecting himself with a rapidly mutating slime mold bioweapon, Young-chul causes a catastrophic outbreak that leads authorities to seal the facility. Among those trapped inside are ostracized professor Kwon Se-jeong, her ex-husband Han Gyu-sung, security guard Choi Hyun-seok, his mobility-impaired sister Hyun-hee, and counter-terrorism leader Lee Bong-seok.
As the survivors navigate the shopping mall, they discover the infected possess advanced swarm intelligence and share sensory information through mycelium. Gyu-sung perishes saving a student, while the remaining group battles both the evolving monsters and their own failing trust. Outside, Gyu-sung's wife, Gong Seol-hee, investigates Young-chul's former laboratory and uncovers crucial behavioral traits about the outbreak's hive mind structure. Inside the locked-down building, the survivors descend to the underground control room, where Hyun-hee aids their navigation via CCTV before sacrificing herself to protect her brother from the encroaching horde.
