S1·E13 The Mark of Satan

Edwyn Rord, a young man working in a hospital morgue, pricks himself with a needle while working on the body of a man who thought he was possessed by the Devil. As a result, the Devil chooses Edwyn as his next disciple - or is it all in Edwyn's mind? In any event, Edwyn becomes obsessed by numerology and kills his mother, and the local Vicar takes a strong line on it all.