The fort is betrayed even of them that should have defended it.

In the Pauline Rite and in some places in the traditional Roman Rite today is the feast of St John Fisher, the cardinal bishop of Rochester. It's also the feast day of St Alban, the first English martyr. St John shares the festal celebration with St Thomas More who joined him in opposing the king's attempts to withdraw England from the Catholic faith. There is a bit more on these three martyrs here with some useful links.

ST JOHN FISHER'S reply to Bishops Stokesley, Gardiner and Tunstal, who were sent to the Tower by Thomas Cromwell to persuade Fisher to submit to the King:

Methinks it had been rather our parts to stick together in repressing these violent and unlawful intrusions and injuries dayly offered to our common mother, the holy Church of Christ, than by any manner of persuasions to help or set forward the same.

And we ought rather to seek by all means the temporal destruction of the so ravenous wolves, that daily go about worrying and devouring everlastingly, the flock that Christ committed to our charge, and the flock that Himself died for, than to suffer them thus to range abroad.

But (alas) seeing we do it not, you see in what peril the Christian state now standeth: We are besieged on all sides, and can hardly escape the danger of our enemy. And seeing that judgment is begone at the house of God, what hope is there left (if we fall) that the rest shall stand!

The fort is betrayed even of them that should have defended it. And therefore seeing the matter is thus begun, and so faintly resisted on our parts, I fear that we be not the men that shall see the end of the misery.

Wherefore, seeing I am an old man and look not long to live, I mind not by the help of God to trouble my conscience in pleasing the king this way whatsoever become of me, but rather here to spend out the remnant of my old days in praying to God for him.