One day in 2012, a group of policemen in a Danish town were sitting around in the office when an unusual call came in. This town, called Aarhus, is a clean, orderly place with very little crime. So what the callers were saying really held the cops’ attention. They were parents, and they were “just hysterical,” recalled Thorleif Link, one of the officers. Their son was missing. They woke up one day and he was gone. The officers put together whatever clues they had about the missing person: He was a teenager who went to a local high school, and he lived in a largely Muslim immigrant neighborhood just outside town. But before they got any further with their investigation, they got another call, from another set of parents. Their son was missing too…..