Michael Gough doing what he does best: be villainous. Handsome in the way that makes you understand why Eve listened to the snake (no offense intended), charming, plausible -- add in the plot, and you have an episode that seems quite modern. The subject matter, serial murder, darkens the tone of the show. And unlike most of the other cases, this is something that has happened in real life (or could).
(And, yes, Gough later went on to join Tim Burton's set of go-to actors. You can see why Burton got hold of him. In an earlier decade, he could have played the Joker, or Two-Face. Or, in a twist, Commissioner Gordon.)