The overarching mystery centers on the 15-year-old kidnapping of young Joo Joong-won. Joong-won spent years believing his teenage love, Cha Hee-joo, died as an innocent victim while an accomplice escaped with a 10-billion-won necklace. In reality, Hee-joo was the vindictive mastermind who harbored intense jealousy toward her identical twin sister, Hanna Brown, who had been adopted into a wealthy family in the United Kingdom.
Hee-joo used Hanna's gentle nature to orchestrate the kidnapping, subsequently tying Hanna inside the getaway car that detonated. Hee-joo assumed Hanna's identity, underwent plastic surgery, and lived abroad in luxury. Secretary Kim Gwi-do, the twins' estranged uncle, stayed by Joong-won's side hoping to uncover the truth. In Episode 15, guided by the spirit of the deceased Hanna speaking through Gong-shil, the living Hee-joo is arrested at the airport, freeing Joong-won from his traumatic reading disorder.
In Episode 12, Joong-won is critically stabbed while protecting Gong-shil from a murderer. As his body flatlines, his wandering spirit confesses his love before fading. Gong-shil saves his life by pledging her servitude to the medium Madam Go, which revives him but erases all his memories of her. Muscle memory and the sun necklace eventually shatter this amnesia. In the finale, Gong-shil departs for a year to understand her powers, returning as a confident woman who purchases her own rooftop building, ultimately reuniting with Joong-won on fully equal terms.