For every teacher, it would be the nightmare come true: An 18-year-old girl named Maybritt goes missing after a school trip to Holland. The girl has vanished without a trace from a tall ship. Did she leave voluntarily? Was it an accident? Suicide? Or did someone help her disappear? Hannah Schmielink, a school psychologist from Münster, discovers that at the Dorenkamp vocational college in Rheine, no one seems particularly concerned about what lies behind the student's disappearance. The classmates remain stubbornly silent, and the faculty is currently only interested in one thing: Who will take over the vacant principal position? When a dead body is found after a school celebration, the first walls begin to crumble. More and more shocking truths come to light. But only when everything seems to be resolved does Hannah learn the whole truth. Just one phone number.