|""A body cannot suffer in sweet repose." - Mary, to Debra"|
She was an "Angel of Mercy" serial killer working as a nurse at a time when Harry Morgan was hospitalized. She was poisoning him with lethal amounts of drugs. As a result, she became Dexter Morgan's first human victim.
Mary killed patients under the delusion that she was "taking their pain away." In 1991, when she tried to kill Dexter Morgan's bedridden father, Harry Morgan. Dexter was given instructions by Harry to kill her.
While Harry Morgan is being treated in a hospital for heart disease, he realizes that his nurse, Mary, is an Angel of Death who is slowly killing him by overdosing him with morphine and an unidentified substance. He gives Dexter Morgan the go-ahead to kill her in order to stop her from killing him and any more people.
Dexter breaks into Mary's house and covers a room with plastic. He dons a full plastic suit with gloves. (Casual clothes are worn underneath.) He waits for Mary to arrive as he holds a syringe (which is ironic because Mary herself killed via syringe). Dexter fails to sedate her in this way, though, and is forced to overpower her in hand-to-hand combat. After he strips Mary of her clothes, he covers her in shrink wrap and secures her to a table with duct tape.
When Mary awakes, Dexter reminds her of her crimes (via her special trophies scrapbook, where she keeps obituaries of her victims). Mary claims that she helped them by putting them out of their misery. However, Dexter throws her words back at her by stating that he is going to take her pain away.
Dexter gags Mary again and repeatedly stabs her, which is quite messy with her blood spraying onto him. He then dismembers her by hacksaw and tosses her remains into the Everglades.
Dexter's intervention prolongs Harry's life another year before he dies (from suicide).
Since Dexter did not take a blood slide from her or dispose of her in the Underwater Graveyard, the police never knew she was a Bay Harbor Butcher victim. An investigation into her disappearance is never mentioned, and it is unknown if the police ever discover her crimes.
- Phoebe Burns (age 60)
- Jason Kheel (age 82)
- David Nammers (age 73)
- Adam_Horrocks (age 42)]
- Adam_Horrocks (age 74)]
- Other victims - Mary had a scrapbook with obituaries of her victims. As Dexter browsed through it, four obituaries were seen in the middle of the scrapbook. It may have contained more obituaries
- Harry Morgan - Mary tried to poison him with an unknown drug mixed with morphine, but he caught onto what she was doing. Harry told her to stop, which made her angry. He then sent his son to kill her as practice in killing more people like her.
- Dexter: "The nurse was my first playmate. I'll always be grateful to her for opening up so many magnificent new doors for me. Things were a little messy in the beginning. Hey, perfecting a new craft takes time. But I was trained well. Those who witnessed my early stumbles never had a chance to tell."
- She had a black cat named Mr. Tinker.
- Mary's last name is never revealed. In the novels, her first name is also absent, and she is referred to as First Nurse.
- Mary is Dexter's first female kill shown in the series.
- Denise Crosby also played a character with the same name in The Walking Dead