‘Dexter’ centers on Dexter Morgan, a forensic bloodstain pattern analyst for the Miami Metro Police Department who moonlights as a serial killer. Set in Miami, the show’s first season was largely based on the novel “Darkly Dreamind Dexter” by Jeff Lindsay, the first of his series of Dexter novels. Subsequent seasons have evolved independently of Lindsay’s works. It was adapted for television by screenwriter James Manos Jr. who wrote the pilot episode.
Dexter structures his killing around “the Code of Harry”, a body of ethics and procedures devised by his adoptive father Harry Morgan (who was a Miami cop) to make sure Dexter never gets caught and to ensure that Dexter kills only other killers. After discovering that young Dexter has been killing a multitude of neighborhood pets for several years, Harry tells Dexter that he believes the need to kill “got into” him at too young of an age, and that he believes Dexter’s need to kill will only grow. To keep Dexter from killing innocent people (and from winding up in an electric chair), Harry begins teaching Dexter “The Code.” In this code, Dexter’s victims must be killers themselves who have killed someone without justifiable cause and will likely do so again. Dexter must also always be sure that his target is guilty, and thus, frequently goes to extreme lengths to get undeniable proof of his victim’s guilt. Most importantly, Dexter must never get caught. Harry also trained Dexter in how to interact convincingly with other people despite his dissociative mental illness, which Harry believed to be sociopathy, arising from Dexter witnessing the brutal murder of his biological mother, Laura Moser. As an adult, Dexter has largely escaped suspicion by being genial and generous and maintaining generally superficial relationships. However, his attachment to his foster (and ultimately adoptive) sister, Debra, his girlfriend, Rita, his stepchildren, Astor and Cody, and later his biological son, Harrison, have all complicated his double life and made him question his need to kill.