Sorcha and Cormac had Victoria Waterfield stay with them while the Second Doctor and Jamie McCrimmon took care of some business. During this time, Cormac, Sorcha and Tadhg succumbed to the Black Death. Niall blamed Victoria, as she had claimed to see a screaming ghost at each death. Niall instead thought Victoria was a witch, and tried to strangle her. He was stopped by the Doctor and Jamie.
The Doctor realised that Niall too had the Bubonic Plague, but as Victoria's blood had picked up antibodies during her travels, the Doctor gave Niall an injection of her blood. He survived the plague. (PROSE: Screamager)