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 stalked 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.

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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.