Derek Ho, Singapore's first serial killer, has been sentenced to death. As he awaits his fate in prison, a team of top psychologists led by Dr Daniel De Silva is assembled to interview him. But Derek refuses to speak to any of them. Dr De Silva calls upon a young protégé of his, Dr Winnie Low, to help him break through to Derek.
Winnie meets Derek for the first time. She manages to get Derek to talk about his first kill, but in her enthusiasm to break through to Derek, she crosses the line and triggers a violent reaction from him
Going through Derek's personal belongings seized by the police, Winnie comes across an old photograph of Derek with a young girl whose face cannot be seen. The investigating officers, Isp Han and SSSgt Razali, cannot provide clues to the girl's identity. So Winne starts digging.
Assignment Derek Ho suffers a setback when Derek attempts suicide in his prison cell and falls into a coma. Meanwhile, Winnie finds out the name of the mystery girl in the photo…Stephanie. But who is she ?
Derek emerges from his coma. Winnie confronts him with the name of the girl in the photo - Stephanie. Derek finally reveals how they met and how their relationship got off to a rocky - and violent - start.
In a reversal of roles, Derek gets Winnie to reveal details of her past and her tormented relationship with her father. Meanwhile, Winnie is staled by Kai, the mentally-unstable former patient who violently attacked her.
Winnie tries to engage the help of the police - in particular, SSSsg Razali - to arrest Kai for stalking her, but no ones seems to believe her. Derek tells Winnie about his own stalking days…finding and then attacking Stephanie's psychiatrist.
Derek tells Winnie about the definitive moment in his relationship with Stephanie. Meanwhile, Winnie, accompanied by her mother, confronts Kai and his parents at his house, but her complaints fall on deaf ears. A vengeful Kai goes after Winnie's mother.
Jacob Fernandez tells Derek his appeal has been rejected and he has to return to prison to face the death sentence. Winnie breaks down and finally reveals what is happening with Kai. Derek tells Winnie to kill Kai.
Derek recalls the final days of his relationship with Stephanie, and how it shaped the killer that he is. Winnie is shocked to discover the person responsible for setting Kai loose onto her.
Inspector Razali goes to Winnie for help – the decomposed body of a property agent, Leong Li Li, has been found in a nature park, and Derek Ho is listed as one of her former clients. Winnie is asked by Razali to find out what Derek knows about Leong Li Li and if he had anything to do with her death.
Derek reveals to Winnie that he knows who killed Leong Li Li, and he will tell her … if she takes him back to Serenity Lane, the house he almost bought from Li Li. Winnie and Razali struggle with the decision to allow Derek out of prison in order to help them with heir case.
Winnie and Razali bring Derek back to Serenity Lane, and meet Jessica Sun (Jessie), a woman whom Derek claims to have had a relationship with in the past. But Jessie denies knowing Derek and Derek clams up. An incensed Razali blames Winnie for leading him on a wild goose chase.
Winnie gets a call from Jessie, who requests her presence at Serenity Lane. There, Jessie reveals two secrets that compel Winnie to stay and listen to her story. Meanwhile, Razali gets called back to prison … Derek wants to see him.
Derek and Jessie tell Razali and Winnie respectively about the relationship they had, and how it resulted in the entrapment and torture of Leong Li Li’s abusive lover, Billy Wong.
Jessie relates to Winnie the incidents that took her down the path of murderous mayhem: their discovery that Leong Li Li was being abused by her boyfriend, Billy Wong, and Jessie’s decision to avenge her torture.
Derek and Jessie lay a trap for the abusive and foul-tempered Billy Wong, but he turns the tables on them and tries to escape. Meanwhile, Winnie learns about the tragedy that changed Jessie’s life forever, taking her destiny down a different path.
Derek helps Jessie carry out a plan of deception. But he realizes this has put him on a path of no return, where he may have endangered Jessie’s life. Meanwhile, Inspector Razali and SSSgt Miki Lee finally have the name of Leong Li Li’s killer … but can they find him in time?
Inspector Razali goes to Serenity Lane to arrest Jessie for the murder of Billy Wong several years back. He is surprised to find Winnie there. A bigger shock awaits the both of them …
Razali and Miki resolve the case of Leong Li Li’s murder, as Derek comes to terms with who he is and what he’s done. Winnie experiences a personal tragedy of her own, while Jessie finally finds peace … or does she?