Episode: "Let's Give the Boy a Hand"
Air Date: 10/22/06
When Rita first appeared on Dexter she was emotionally distant and sexually withdrawn as a result of her previous marriage to a fiend who abused both drugs and her. She was perfect for Dexter, who at first only wanted a beard and not a real relationship.
Season one sees Rita gradually emerge from her shell, starting with Halloween, when she abandons her typical Snow White costume for Lara Croft's tomb-raiding getup (which Dexter points out would actually be ill-advised clothing for raiding tombs) to turn Dexter on.