Not My Blood (Paperback) by Barbara Cleverly

Scotland Yard Detective Joe Sandilands is caught off guard one night in 1933 by a phone call from a distressed boy named Jackie Drummond, who just might be the illegitimate son Joe never knew he had. Jackie is in trouble at his Sussex boarding school, where a teacher has been murdered. When Joe gets himself assigned to the investigation, he learns the boarding school case is more complicated than it appears: A frightening number of boys, all from wealthy families, have gone missing over the school’s history, and by some coincidence none of the families have followed up on their sons' whereabouts.