At Chartley Manor in England, Mary, Queen of Scots exchanged enciphered letters with Anthony Babington's conspirators through a covert channel controlled by Francis Walsingham's agents. The messages were decoded, and a postscript requesting the names of assassins was added by a government cryptanalyst. The correspondence supplied evidence used at Mary's trial.

The episode made letters, codes and disputed textual evidence central to Mary's tragic legend. It influenced historical drama, novels and poetry about surveillance and betrayal, while the deciphering work of Thomas Phelippes became an early landmark in the literary history of secret writing.