Highlander: The Series - Season 1 Episode 20
Avenging Angel

When fatal stabbing fails to kill him, Alfred Cahill becomes convinced that he has been chosen by a higher power to wage a crusade against perversion, and cuts a bloody path through Paris, murdering prostitutes and pimps, and endangering an old friend of Tessas who has become a call girl. MacLeod tries to explain Immortality to Cahill, but he cant get through to him, and finally is forced to take his head.