In July 1996, 13-year-old Caroline Dickinson was on a school trip in France, staying at a youth hostel where she was raped and murdered - the killer escaped without anyone raising the alarm. The police arrested a homeless man who confessed to the crime, but by the time DNA tests had eliminated him, the train had gone cold. This is the story of how Caroline's parents refused to let the case rest, and how a US Customs officer helped track down Francisco Montes, their daughter's killer.