At a trendy gallery opening, Ryan, a well-dressed and attractive man, notices a mysterious brunette woman in a black hat. He briefly morphs into a Fuchsbau (fox creature) as we see him approach her, ready to lay on the charm. The woman has a quick tongue and coyly plays against his advances, leaving the gallery and leaving him wanting more.
He follows the woman, Lena, outside and manages to talk her into his stylish apartment. When she tries to leave, Ryan attacks her, throwing her down onto the couch. Imagine his surprise when Lena turns the tables and pins him down, morphing into a terrifying spider creature. Ryan tries to fight back and even manages to bite off one of her fingers, but he's no match for Lena's spider form. She regurgitates a milky liquid, forcing his convulsing body to swallow it. Later, Lena emerges from the apartment, her hair a mess and her face smeared with blood, horrified by what she's done.
Nick and Hank arrive at their latest crime scene to find Ryan's dead body completely desiccated. Nick and Hank are stumped; that kind of deterioration doesn't happen overnight, but his girlfriend talked to him on the phone the night before. Additionally, video surveillance from the gallery confirms that he was alive. Nick and Hank note him talking to the woman in the black hat, the question is... did they maybe meet up later after the event?
Later, Harper examines the dead body and explains her discovery to Nick and Hank. The body was forced to ingest a highly corrosive acid, killing the victim from the inside out. The acid, suspiciously enough, is found in spider venom. Then, the victim's organs were sucked out by some mechanism that left a bite mark, literally sucking him dry.
Lena enters an upscale bar, this time, as a blonde. She sets her sights on a nicely dressed man dining alone and goes in for the kill. Later in a dark hotel room, Lena attacks the man the same way she did Ryan, forcing him to ingest the corrosive white acid as she morphs into a terrifying spider creature.
After investigating Aunt Marie's books, Nick discovers a spider creature that seems to match their suspect. He goes to Monroe with his suspicion and learns about Spinnetods, the Black Widows of the creature world. Monroe doesn't know much but says he has a contact who might be able to help out Nick. He takes Monroe to visit Charlotte, an old woman Spinnetod who turned her back on who she was years ago. She's actually 26 years old but appears 70; her condition causes rapid aging. The only way to stop the curse is to kill and suck the life out of young men. It must be done every five years, three victims at a time.
Nick takes Lena's prints from the house and finds that they somehow match that of the severed finger from the original crime scene. While they can't fathom how it's possible, this is reason enough to take Lena into custody. They arrive at her house, but it's too late; Lena's already left for her third kill. The police track her to the Marina, where she's seducing a young man on his boat.
Later, after the game, Lena gives her husband the gold Rolex watch she took off Ryan's dead body as a gift. They share a passionate kiss; despite her horrible nature, it seems their love is true and genuine. Entranced by the watch, their young daughter takes it from her father's nightstand and takes it with her to school, showing it off to her classmates. When the principal reports her having the watch, the tracking number leads the police back to Lena. When Nick goes to question Lena, he notices her bandaged finger and is sure he's got her cornered. But when she unravels the bandage, her finger is there, intact.
The police intercept the young man and find Lena, who viciously attacks Nick, trying to make him her next victim. He fights her off and manages to trap her in a net, ironically leaving her in a tangled web. Later, Nick and Hank go to escort Lena's confused and worried daughter. Nick sees her morph into a young Spinnetod and is fearful of the cycle that will inevitably start with her as well. Meanwhile, Lena rapidly ages in the holding cell, faced with old age since she was unable to get her third kill.
As the second victim is discovered, a match is found on the fingerprints at the scene. The prints are linked to a similar killing of three victims in another state five years before and an identical case five years before that. There seems to be a pattern, and only two have been killed so far. That means Nick and Hank don't have much time to track down their killer before a third man is found dead. Meanwhile, Lena removes her wig and makeup and greets her husband at her daughter's soccer game. As it turns out, our cold-blooded killer is also a soccer mom.