Mary Stockton was one of two women imprisoned by the Japanese at Cotabato in Biggles in Borneo. A daughter of a British Consular officer, her father had been in London making a report when the Japanese attack began and so she was captured alone. She was engaged to Jackson, a British diplomat stationed at Manila. At Cotabato, she was kept with Doctor Harding, an American woman, in a house on the hillside, separate from the male prisoners who were kept in the local civil prison.
When Jackson, Bill Gray and Pat Flannagan made their escape bid from Cotabato, it had been Jackson's intention to free the women but the alarm had been raised and they were pursued before they could reach the women's house. Later, during Biggles' raid on Cotabato, Jackson succeeded in getting the two women. They were taken to Lucky Strike on the Cayman and then by the Liberator to Australia.
Mary had a passive role in the plot. Not much is made of her engagement to Jackson. The reader is not even treated to a line of dialogue between her and her fiance.