In The Vanishing Triangle, investigative journalist Lisa Wallace publishes an article about her mother's murder, which sparks the disappearance of Amy Reynolds. Alongside Detective David Burkely, the two work together to find Amy. Their investigation takes them around Ireland, as more girls go missing. As they follow every lead, some end up dead ends, but all the while, the killer plays psychological torture games with Lisa, putting her in compromising situations. As they get closer to finding the killer, David and Lisa learn more about the long-rooted corruption in the Gardaí system. To cover their tracks, high-ranking Gardaí members blackmail David with his own secrets. The investigative trail finally leads Lisa to the killer, where they face off again after all these years. In the end, she must confront her childhood trauma in order to save the missing girls.