1. Barton, George. 1919. Celebrated Spies and Famous Mysteries of the Great War. Boston, MA: The Page Company.
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2. Boghardt, Thomas. 2004. Spies of the Kaiser: German Covert Operations in Great Britain during the First World War Era. St. Antony’s Series. Houndmills, Basingstoke, Hampshire, UK: Palgrave Macmillan.
3. Hieber, Hanne. 2005. “‘Mademoiselle Docteur’: The Life and Service of Imperial Germany’s Only Female Intelligence Officer.” Journal of Intelligence History 5 (2): 91–108. doi:
10.1080/16161262.2005.10555119
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4. Macrakis, Kristie. 2014. Prisoners, Lovers, & Spies: The Story of Invisible Ink from Herodotus to Al-Qaeda. New Haven, CT: Yale University Press.
5. New York Times. 1918a. “Spy Net Yields 2 Women Here; Men Also Taken.” New York Times, March 19, sec. News.
http://query.nytimes.com/search/sitesearch/
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