Two men lie in a hospital room, victims of apparent sexual assault. Curiously, both are also suffering from severe electrical burns. Tom Baxter was found in an alleyway, unconscious and discharging 215 volts of electricity. Fred Sylvain was brought into the shock ward registering a reading of 40 volts. As the OSIR team investigates the case, Axon notes that while humans are electrical conductors, the storage and discharge of electricity is extremely rare.
Dr. Diane DeLuca administers to the patients, as Praeger and new team member, parapsychologist Mia Stone check out the charred accident site. When Stone's voltage meter indicates that nothing in the alleyway is discharging high voltage, Axon and Praeger conclude that, considering the charred regions of the victims' bodies, the burns likely happened during sex. As the investigation continues, a witness comes forward saying that she had seen a woman with "big" hair, sexy clothes and high black boots exiting the alleyway just before she found Baxter laying burned and unconscious. Meanwhile, Sylvain is convinced that his attacker was a succubus, which, Donner explains to her colleagues, is a lascivious she-demon believed to copulate with men in their dreams.
When the team goes undercover to track down the attacker, Praeger goes missing - and becomes her third victim. Later, a trembling Praeger cowers in the alley, his lips red and raw. He looks up in horror to find Diane DeLuca staring down at him. Visible in a bag next to her are a wig and shiny black boots. Diane flees the scene, leaving Praeger behind.
Back in the hospital, as Diane cares for Praeger, the team members struggle to find a clue the string of incidents. When Stone remarks that the most common cause of human electricity is lightning, Donner does some checking with the Weather Bureau. She is stunned to discover that, during an electrical storm in the area 10 days ago, DeLuca was reportedly struck by lightning. Further digging into her medical records reveals that she has been diagnosed with Female Sexual Arousal Disorder. Shocked that Dr. DeLuca could be the perpetrator of the attacks, the team also realizes that the doctor could now be treating her own victims.
Needing to release the electricity building up inside her, DeLuca finally turns to her ex-boyfriend, Dr. Russ Turnbull, who is surprised and excited by Diane's apparent change of heart. But as he pulls her close and kisses her passionately, he is suddenly thrown back against the wall by a jolt of electricity.
Still desperate, DeLuca races to find another victim. She suddenly buckles over and screams in intense pain. The OSIR team quickly transfers her to the lab where they discover that she is discharging an alternating current of 250 volts. Their only choice is to neutralize the current, flush her system and drain the electricity out of her - and they must act quickly. With DeLuca's electrical impulses increasing rapidly, will they be able to save her before her system overloads?