Manuel d'Andrada was a spy for King Philip II. He gave Lopez a ring as part-payment for poisoning the Queen. Andrada was recruited as a double agent by Lord Burghley. Essex uncovered the plot.
The spies of Essex infiltrated Andrada's group and uncovered the assassination plot.
Burghley knew that Andrada and Lopez were probably plotting to murder Dom Antonio who had become an embarrassment. However, he was prepared to turn a blind eye in return for information about plots against the Queen.
But Andrada was involved in a plot to murder Dom Antonio and Queen Elizabeth and he'd approached Lopez to do the deed. After Andrada's release by Burghley he lived with Lopez briefly. For two or three years they haggled over a price for the assassination of the Queen. Lopez would agree a price but later ask for more. Eventually Andrada left when he felt that the plot was becoming public.
Two double agents replaced Andrada but were captured. One of them wrote to Lopez to ask for help. Lopez replied with a letter of support, a letter that was instrumental in convicting him.
A memo to the King of Spain contains a request from Manuel d'Andrada for a jewel to pay Lopez. In another letter dated 30.4.1587 to the Spanish ambassador, a Spanish agent writes that he'd approached Lopez, asking him to poison Dom Antonio.
Lopez had plenty of private information from his important clients that he could trade. As Dom Antonio's position got weaker, the Spanish decided to use Lopez to catch a bigger fish - Queen Elizabeth I.
A contemporary note by Francis Bacon claims that the two double agents, Stephanus Ferreira and Edward Loisie, confessed to the conspiracy to poison the Queen:
"Stephanus Ferreira confessed that Count de Fuentez and Ibara had signified unto him both by letters and word of mouth that there was a plot layd to take way the Queenes life by poyson; that hee wrote letters by Lopez his dictating wherein he promised the same, conditionally that 50000 Duckets should be payed unto him; also that Emanuel Loisie was secretly sent unto him by Fuentez and Ibara, to excite Lopez to dispatch the matter speedily."
However, Bacon was working with the Earl of Essex at the time, so it was in his interests to see Lopez convicted.
Q. What problems arose from having a female monarch?
The most pressing problem in England in the late 16th century was that Elizabeth had refused to marry and so had not produced an heir. What reasons would she have for staying single? To answer this we need to ask what kind of status a married woman had in respect of her husband. Nor was the experience of Elizabeth's relations encouraging. Her sister, Mary, had married Philip II of Spain in one of the most politically disastrous marriages an English monarch has ever made. Mary Queen of Scots' rapid turnover of unreliable husbands provided an equally poor model.
Why, having refused to marry and have children, did Elizabeth also refuse to say who was going to succeed her? Did the uncertainty about who would be next on the throne exacerbate the spying and whispering, and the naked ambition, of different factions? And Burghley, Robert Cecil and Essex not only had to try and manipulate the situation in the English court, they had also to work on the court of James VI of Scotland who had the best claim to the succession. In the circumstances the air was inevitably thick with plots.