In Biggles in the Blue, Dr Douglas was the doctor who attended Werner Wolff, an ex-Nazi, who had been residing in Rumkeg Haven, a villa on the outskirts of Kingston, under an assumed name of Christen Hagen. Dr Douglas had told Wolff that he had thrombosis and had advised him to put his affairs in order as there was nothing that could be done about the condition and he might die suddenly. Hagen apparently accepted the advice and began writing a letter to Erich von Stalhein but died before he could pen down exactly where he had hidden some important papers. Douglas was summoned by Josephine, Hagen's house-servant when she discovered that her master had died. Douglas then summoned the police with a view to discovering the next-of-kin. The police search of Rumkeg Haven subsequently discovered the true identity of Hagen and alerted the authorities in London.