She had also changed her ciphers .
The English ambassador in France , Nicholas Throckmorton , discovered that Mary of Guise had obtained details of the plans for the 7 May assault .
Mary of Guise had also changed Mary of Guise 's ciphers .
The English ambassador in France , Nicholas Throckmorton , discovered that Mary of Guise had obtained details of the plans for the 7 May assault .