When four-year-old Mara Vale vanishes from a beach changing room, her eight-year-old brother, Eli, spends the rest of his life believing he failed her. Thirty-eight years later, a cold-case detective finds an unfiled teenage confession hidden in an archive box. It contains one detail nobody outside the family should know: the silver crescent Mara had drawn on the corner of her blue towel. Eli and Detective Nora Bell follow the confession back to a vanished marshland, a buried road, and a development built over the place where the truth may have been erased. But when the case finally reaches court, the evidence that could name Mara’s killer may be the one thing the jury is never allowed to hear.