One of the most dramatic crimes that many of the seven were accused of was the capsizing of the Erskine ferry. This was said to have been carried out shortly after they had met at John Hardie's yard in Dumbarton in order to burn the minister's effigy, resulting in his untimely death. They travelled the short distance to the south very quickly, and in the company of the devil made their plans.

Some of the witches were reluctant to commit this particular crime, given that they knew John Glen the ferrier personally, but they were overruled by one of the crew who held a personal grudge against him. They were said to have watched while the ferryman helped a member of the local gentry, the laird of Brighouse, aboard, as well as several horses. With the help of the devil, they caused the boat to capsize, resulting in the drowning of both men and the animals.

The ferry did indeed capsize, and both men lost their life in the incident. It was another unexplained incident in the local area until it was confirmed by various confessants that witchcraft lay at the root of the event.