Two voices tell the story in What She Knew: protagonists Rachel Jenner and Detective Inspector James Clemo of the Avon and Somerset Constabulatory. Their lives entwine when Rachel’s eight-year-old son, Benjamin Finch, goes missing on a Sunday afternoon in a local park. Still struggling to accept the divorce that shattered her family, Rachel is distracted that day, impulsively agreeing that Ben can run ahead to their destination with his dog, Skittle: “He didn’t stop or look back at me. And that was the last time I saw him.” Ben is just gone, nowhere to be found, as Rachel is plunged into a nightmare that seems never to end.

The case of the missing boy is assigned to DI Jim Clemo, who is thrilled at the opportunity to prove that he is capable of handling a major case. In his enthusiasm, Clemo proffers Detective Constable Emma Zhang to act as FLO (Family Liaison Officer), their romantic relationship kept rigorously secret from coworkers. Jim is confident in Emma’s ability to act as FLO and pleased to assist her in expanding her career options. The consequences of this decision will weigh on the detective’s heart long after the case is resolved, one of many factors that burden him. Ben’s disappearance proves a particularly difficult case as days pass with little progress, a growing list of people remaining to be interviewed.

The first jarring note of an investigation gone awry is Clemo’s bumbling of his first official assignment: the press conference with the boy’s mother. Rachel proves unable to follow the script provided as the cameras roll, an inappropriate emotional outburst alienating the kidnapper and inspiring unwelcome curiosity, the beginning of a growing rumor that Rachel may have actually harmed her son. Social media feeds a tide of innuendo and suspicion, a Greek chorus of malicious opinions. The public demands an answer, increasing the pressure on authorities for a resolution.

The case unfolds in chapters that segue between Rachel’s ordeal and Clemo’s therapy sessions after the investigation closes, the detective overwhelmed by stress, his inability to save the boy and the personal issues complicating a successful resolution. In contrast, Rachel Jenner endures the agonizing process of waiting for an answer, anxious that she has not done enough to find Ben or given the wrong impression to an avaricious media. Her dependence on her best friend, Laura, and her sister, Nicky, turns to mistrust as the days pass, self-doubt and fear growing as harassment thrives in the wake of that disastrous press conference.

In her first novel, Macmillan captures the essence of a police investigation, one that is emotionally loaded for the desperate divorced parents. The authorities cast a wary eye on the mother as they narrow down the list of suspects, fears of Ben’s death accelerating with each dead end. In a nod to contemporary realities, the author explores the power of social media on current events, the situation exacerbated by a critical blog that questions the mother’s motives and reveals information about the case not available to the public.

Both protagonists are flawed, overwhelmed with a surfeit of emotions and the demands of the case. Rachel doubts herself; Clemo is frustrated that he has not found Ben, the pressure from the public mounting with each passing day. At nearly five hundred pages, the details of the protagonists’ experiences are sometimes overdone, especially Clemo’s emotionalism and inability to maintain objectivity. This tendency to overwrite the internal dialog can be refined with time, Macmillan keeping her plot on target as characters and events fall into place, a young boy’s fate finally revealed, the consequences touching all who have endured a painful wait.