Major Thomas Weir was known for his piety and religious fervour, preaching to the masses of the West Bow of Edinburgh.

One Sunday morning in 1670, instead of Weir's usual sermon, he instead confessed to many evil deeds; witchcraft, necromancy, and terrible intimate acts with his own sister Grizel. After claiming that he had made a pact with the devil the Weir siblings were arrested, accused of witchcraft and incest.

Grizel recounted stories of devilry and magic including one occasion, when a blazing carriage led by charcoal horses arrived at their home on the West Bow to take them to their master, Auld Nick himself.