Philip Marlow Sidney, A history of the gunpowder plot… (1904)
“ After consulting with Mounteagle, the latter probably went to Lord Salisbury, and all arrangements were made accordingly. It may be argued that if Salisbury knew of the existence of the plot, why should he have exacted the performance of such a farce as the production of this letter? But all the evidence tends to show that the letter was designed for Mounteagle's own protection, and that he could see no other way of clearing himself from being considered a traitor to his friends than by obtaining an anonymous warning of the kind actually received. ”
