On a blistering Boston summer day, a nine-year-old girl disappears while crossing a public park. The only witness is a homeless schizophrenic woman who believes she is under surveillance and whose memory may not be reliable. Dr. Paul Lucas, an expert at interrogating violent criminals and the insane, is called in to help evaluate the woman's testimony.
Lucas elicits small details that lead police to three people with no apparent connection: a retired engineer, his disabled wife, and a young man who works at a doughnut shop. But interviews with each suspect go nowhere, frustrating detectives and calling into doubt Lucas's role in the case. Believing the girl is alive but without water and soon to die, he is pushed to the brink of a professional abyss--under intense focus from local media, distrusted by police, and pressured by his wife, Abby, whose stake in the search is deeply personal.
With time running out, Lucas has to make a choice: to honor and uphold the sworn central oath of his profession, or to cross the line and do whatever it takes to find the girl, even if he must crack the mind of a vulnerable patient.