Nikki Wald is a Character and Serial Killer in DEXTER. She along with her boyfriend Johnny Rose are responsible for a series of murders dubbed the Vacation Murders, thus dubbing them both as "The Vacation Murderers".
Nikki is shown to be a young, Caucasian woman with long black hair. She wears a sleeveless yellowish green top underneath an unzipped, pink long-sleeve jacket atop a set of short bluejeans with what appears to be brown shoes.
Though not much has been shown with her character apart from the way she and her boyfriend kill people, she is shown to be a very violent and unstable individual who acts on reaction whenever something terrible happens to her, which is due in part to her addiction to meth. This can be seen clearly when she hears about Johnny's syphilis and multiple partners and ends up killing Johnny. Of course, even after she kills him she has hallucinations that she is still in the hotel with Johnny talking over his dead "body".
She first met Johnny Rose in high school and began a shoplifting crime spree with him before the fourth season where she was eventually caught with Johnny and later testified against him for a reduced sentence. At some unknown point in time Johnny and Nikki rekindled their romance and made a plan to rob people so they could buy a boat and sail off into the sunset. They would later become famous for these crimes as they tended to target tourists, thus earning them the nickname "The Vacation Robbers".
This series of crimes later escalated to murder after one of their victims interrupting them and was incidentally killed in the struggle. After this incident they changed their way of operating, beginning a new spree of killings that got their nickname changed to the "Vacation Murderers". Soon after they committed another murder and took every thing they could find, but later the law caught up to them after Johnny accidentally cut himself on a cactus leaving blood evidence. Because of this Lieutenant Maria LaGuerta and Sergeant Angel Batista come to Nikki's apartment to question her when Nikki and Johnny were just getting home where they opened fire on the officers and took off in a grey sedan.
It is not until the fifth episode of the season that they are finally caught after they are suspected of gunning down Frank Lundy and Detective Debra Morgan with Lundy dead and Morgan alive. Sergeant Batista takes advantage of a reporter, Christine Hill, by telling her about Johnny's syphilis and multiple partners in an attempt to cause a rift in their relationship. When Nikki sees the news article however, she overreacts and ends up killing Johnny and hallucinating until she is eventually tasered by Detective Joey Quinn in a back alley.
In episode six, she confesses to the Vacation Robberies and Murders, but not to shooting Debra and Lundy. Debra confronts Nikki about the shooting and after a long conversation Nikki is able to convince Debra that she had nothing to do with Lundy's murder, even after Debra threatens to lie saying that she did see Nikki that night. After this it is presumed that Nikki is sent to prison as she is never seen again in the series.