Between 1593 and 1594, agents uncovered an alleged plot by the Queen’s own physician, Dr. Rodrigo Lopez. Lopez had been in secret contact with the Spanish court and was accused of scheming to assassinate Elizabeth. In 1588, Spain had dispatched a 130-ship naval fleet as part of a planned invasion of England. The invasion failed, but with the invasion fresh in people’s minds, it was easy to imagine that the accusations against Lopez were true. Despite Lopez’s protestations of innocence, he was executed for treason.
https://www.history.com/news/queen-elizabeth-spy-network-england