Mary Stuart was held captive in England for about 20 years. During that time, she secretly tried to regain liberty and her crown. While appearing to live a tranquil life, she was conspiring to be set free, corresponding with the ambassadors of France and Spain, with the Pope and with her supporters in Scotland and Holland. Secret signs and secret codes were invented that were changed monthly. She used these to correspond with all of Queen Elizabeth’s enemies. Letters were hidden in linens, books, hollow canes, the lids of jewelry boxes, sometimes even in mirrors. In books that Mary sent to Paris or London, a code was established to find letters on certain pages that spelled out messages. Lord Cecil however, ran a police state, and everyone was under surveillance. He eventually used a series of double agents to trick Mary into agreeing with a plot to overthrow Elizabeth. This was the Babington Plot, and it was what led to her execution.