Carpenter plays Dexter's sister, Deborah, who worked her way up to detective in the Miami PD -who always craved the attention of her late father, Harry (also a detective). But Harry was too busy teaching Dexter his "code" for satisfying his bloodlust while not getting caught.
In season 4 we find Dexter married to Rita, stepfather to Cody and Aster, and new father to Harrison. True to form, Dexter finds a way to get out of one sticky situation (almost getting caught) after the other while balancing his new family life. The intensity of each episode never wanes; each are treated like a finale, and I really appreciate the writers pushing the envelope this season. There are also many appearances of Dexter's deceased stepfather, Harry (his Jiminy Cricket), as Dexter starts to separate from the "code" when it conflicts with his new priorities as a father.