Highlander S01E20 - Avenging Angel

When a fatal stabbing fails to kill him, Alfred Cahill becomes convinced that a higher power chose him to wage a crusade against 'perversion'. He cuts a bloody path through Paris, murdering prostitutes and pimps, and endangering an old friend of Tessa's, Elaine Trent, who has become a call girl. MacLeod tries to explain Immortality to Cahill, but he can't get through to him, and finally is forced to take his head.