In The Case of the Secret Inquisitors, Doctor Kahn was a scientist who organised the kidnapping of important scientists and officials, subjecting them to his mind-manipulation techniques in order to extract secret information from them and, if necessary, programming them with ideas and thoughts of the doctor's choice.
Biggles met Kahn by posing as an important scientist and getting kidnapped and brought to the private sanatorium somewhere in Britain where Kahn conducted his experiments. Kahn told Biggles that he did not work for any particular country. He belonged to a master-group that was interested in revolution in Britain. He extracted information to sell to hostile powers to fund his research. His earlier experiments involved "emptying the mind" of victims, extracting information from them and reducing them to "empty shells". Later, his techniques evolved and he was able to "program" his victims with thoughts and ideas of his choice. Among his victims were Pierre Lefebre, Adamson, Peter Bard and Maxwell Harrington. Biggles overpowered Kahn and escaped from the sanatorium, returning with a large group of police to put an end to Kahn's operation.