Across eight episodes, the narrative unmasks Yun-o as a prolific predator who uses high-end architectural sites to dispose of his victims. Gi-eun’s brush with death in the reservoir sets her and Mok-won on his trail. When Sum interacts with Yun-o, she rapidly pieces together that he is the killer using her algorithm. Instead of alerting authorities, Sum aids him, fascinated by a man who mirrors her inner void.
The tension culminates when Yun-o threatens Mok-won and Gi-eun, attacking Mok-won's shrine and proving he is an untamable threat. In Episode 8, Sum arranges a clandestine rendezvous at an unfinished architectural project. Sensing the trap, Yun-o attends anyway, driven by his fixation on her. Sum ambushes him, using a box cutter to slice his eyes and slash his jugular. Yun-o dies in agonizing intimacy, gazing at her with strange fulfillment. Sum washes away the blood, faces no legal repercussions, and returns quietly to her coding console.