A brutal murder case causes twin sisters to be reunite again. Their life trajectories, which are like parallel lines, get intertwined. They exist in different realms when they meet again. Due to investigation into an explosion case, Hong Kong police officer Yuen Sing-kit reaches Singapore. His girlfriend Leung Hei, an insurance claims investigator, is missing. While cracking down on people smugglers, Singapore STAR Wei Xiao Chen discovers her younger sister Leung Hei’s dead body. Wei Xiao Chen’s sister’s tragic death causes her to recall her childhood memories. To catch the perpetrator and find the truth, Wei Xiao Chen goes to Hong Kong. She disguises herself as Leung Hei and investigates people around Leung Hei. When the conundrum is about to be deciphered, she finds out Leung Hei’s death had implications for other crimes. Wei Xiao Chen gets further from the truth as investigation progresses. The darkness behind the crimes is bottomless.