BBC - More has been discovered about the life and curious times of a World War I "unknown heroine", whose spycatching exploits were found in the archives of the Royal Society of Chemistry.

This unsung heroine, who spoke German and Dutch, had worked as a censor during the First World War and in 1915 had found a letter being sent to Holland with secret messages in invisible ink.
The discovery of these messages, written with lemon juice and formalin, detailing military movements, prompted the arrest of a suspected German spy, Anton Kuepferle. But before his trial had been concluded, the accused spy was found hanged in his cell, after apparently using a silk scarf to kill himself. He was said to have left a message admitting that he was a German officer. (Suicide. Silk scarf. Confession?!?! Are you buying this?) (more)