Well, this is a good a starting point as any for background to my recent CoC Dunwich scenario:
664. Eclipse and plague
Bede (HE, iii.27) reports in 664 an eclipse and a sudden pestilence which raged far and wide in southern Britain, Northumbria, and Ireland.
The Venemous Bede also writes this:
THE EAST SAXONS, DURING A PESTILENCE, RETURNING TO IDOLATRY, ARE IMMEDIATELY BROUGHT BACK FROM THEIR ERROR BY THE BISHOP JARUMAN. [A.D. 665.]
At the same time, the Kings Sighere and Sebbi, though subject to Wulfhere, king of the Mercians, governed the province of the East Saxons after Suidhelm, of whom we have spoken above. That province laboring under the aforesaid mortality, Sighere, with that part of the people that was under his dominion, forsook the mysteries of the Christian faith, and turned apostate. For the king himself, and many of the Commons and great men, being fond of this life, and not seeking after another, or rather not believing that there was any other, began to restore the temples that had been abandoned, and to adore idols, as if they might by those means be protected against the mortality. But Sebbi, his companion and co-heir in the kingdom, with his people, very devoutly preserved the faith which he had embraced, and, as we shall show hereafter, ended his faithful life with much felicity.
King Wulfhere, understanding that the faith of the province was partly profaned, sent Bishop Jaruman, who was successor to Trumhere, to Correct that error, and restore the province to the truth. He proceeded with much discretion (as I was informed by a priest who bore him company in that journey, and had been his fellow laborer in the word), for he was a religious and good man, and traveling through all the Country, far and near, reduced both the aforesaid king and people to the way of righteousness, so that, either forsaking or destroying the temples and altars which they had erected, they opened the churches, and rejoiced in confessing the name of Christ which they had opposed, being more desirous to die in Him with the faith of the resurrection, than to live in the filth of apostasy among their idols. These things being performed, the priests and teachers returned home with joy.664 is also the year of the Synod of Whitby when the English bishops got together to discuss the date of Easter and haircuts for clerics.