Brennan, working hard on her latest novel, is enlisted by Booth to help locate and identify the remains of Charlie, a 6-year-old who went missing from a local park. Brennan determines that Charlie was sexually assaulted before he was murdered, which leads Booth to conclude they're on the hunt for a serial pedophile. When the prime suspect is eliminated, Booth and Brennan pay a heartbreaking visit to Charlie's mother, Margaret, to inform her that Charlie's killer is still on the loose. Suspicion creates uncertainty - among even the people closest to Charlie - and Brennan and Booth must investigate all leads, no matter whom the information points to.