The Twenty Third is a murder mystery that switches between past and present timelines of a serial killer's path of destruction and the aftermath years later. Olivia Dartley is living a low-key life in New York City. She is a successful author and is trying her best to forget the horrors of her past, even though, she never truly can get away. Olivia’s ex-boyfriend, Nicholas Whittaker, is an infamous serial killer known as The Belle Murderer. When she was in her twenties she helped get him convicted and thrown away for life, or so she thought.