Herr Heidegger was the German teacher at The Priory School, run by Dr Thorneycroft Huxtable. When Dr Huxtable employed Sherlock Holmes to solve the mystery of the apparent kidnapping of young Lord Saltire, son of the Duke of Holdernesse, Holmes discovered that Herr Heidegger had also disappeared from the school, as had his bicycle. He therefore became a prime suspect, but when Holmes followed the tracks from Herr Heidegger's bicycle they led him to the teacher's corpse lying on the moor with its head smashed in. Holmes realized that Heidegger had noticed the boy leaving, and had attempted to follow him; however, the real kidnapper had killed him.