The Demon came home and he declared that the air was not clear. "I smell the flesh of man."
In the forest outside of Portland near Mt. Hood, Jill Prembrey is surprised to discover active fumaroles. As the geologist for Eon Industries collects samples, Jill records everything and notes that the existence of the fumaroles is extremely rare. She hears someone moving in the forest behind her and goes back to her truck. A man, Marcus Hemming, grabs her pack of rocks and tries to take it away, insisting it doesn't belong to her. Jill nails him with pepper spray, grabs the rocks, and drives off. She calls her boss, Thom Evans, and tells him what happened as she comes back in.
On the road behind Jill, Marcus transforms into a bull-like Wesen, a Taureus-Armenta.
At the station, Nick and Wu both hover over Hank as he works at his desk. Renard comes over and they all three tell him to get out for three weeks. They figure that Hank is stalling and wheel him toward the door for his first vacation in four years. Everyone waves and then goes back to work.
Juliette returns home and looks around nervously. She makes her way to the kitchen but turns, startled, when she has another memory-flash of Nick cooking at the stove. More memories of Nick appear, all overlapping, and Juliette screams at them all to stop before running out the door to her car and driving away. Another Nick-memory appears and Juliette loses control of the car when she tries to hit it.
In Vienna, Adalind is in her hotel room vomiting because of her pregnancy. Frau Pech arrives and Adalind reluctantly lets her in. She tells Adalind that they have a meeting with the Zigeunersprache: the queen of the Schwarzwald Gypsies. Adalind refuses to go but Frau Pech says that she needs to go if she wants to learn the true value of motherhood and find out how much her child is worth.
When Nick hears about Juliette's accident, he goes to the hospital and she mistakes him for another memory at first. Once he convinces her that he's real, Juliette insists that Rosalee did something to her and now she sees Nick everywhere. She tells Nick that she can't see him anymore and Nick reluctantly leaves.
When Jill arrives home that night, the house shakes briefly and she assumes that it's a tremor. She hears something burning in the dining room and goes to investigate. The glassware has melted and the wallpaper is starting to char. A flaming creature lunges out of the next room and grabs her...
Nick is at Bud's place watching soccer with Bud and Eddie. They soon realize that he's not paying attention and sympathize, saying that they've all been dumped. Nick isn't comforted and says that he's calling it a night. Before he can leave, Nick gets a call about Jill's death and heads to her house to investigate.
Once she's released from the hospital, Juliette goes to see Pilar, who immediately realizes that her memory problems are getting worse.
Nick arrives at the Prembrey house and Wu brings him up to speed. Jill was supposed to pick up a co-worker but didn't show, and the co-worker called it in. Jill has been hideously burned, hand marks branded into her arms and neck. There are the same burn marks on the back door and everything is melted. Wu finds Jill's camera and they play back the video from Mt. Hood.
Juliette describes her problem to Pilar and has her drink a drug that will help her focus. She explains that as Juliette's missing memories are returning, they're too much for her to handle. Pilar tells Juliette to choose the memory that she wants and try to be in the moment with it. To do so, Juliette must go home despite her reluctance or she'll have no future.
Frau Pech drives Adalind to the Gypsy camp and brings her to the Zigeunersprache, Stefania Veduva Popescu. Adalind introduces herself and Stefania escorts them into her tent. She explains that to establish the value of the child, she must determine its bloodline... and there's only one way to be sure. Stefania has her sons hold Adalind while they take some of the blood of the child with a large syringe.
The next day, Nick and Wu visit Thom Evans at Eon. He explains that Jill was one of their best workers and gives them the location where she was working. Thom also tells them about the attack that Jill reported and says that they reported it to the state park police. Nick confirms that Jill was taking rock samples and measuring chemical contents. Thom drives them out to the site. As they go to the fumarole, he admits that they've had a few protestors. The vent is still active and Thom warns that it's a sign that the volcano is becoming active.
Nick senses that something is wrong but can't pinpoint it. Thom pockets a few rocks and they go back to his truck. When they get there, they discover that someone has thrown rocks through the truck windows. As Wu calls it in, Nick hears something again and goes into the woods. He finds Marcus and orders him not to move, and the Wesen woges into his Taureus-Armenta form. After a moment he turns and runs, and Nick chases after him while calling for Wu. Wu catches up to them and tackles Marcus, and as they secure him he screams that they're all going to die because they didn't show respect.
Stefania tests the blood and tells Adalind that she was right about the child being a Royal... and they don't have to kill her. The Zigeunersprache offers a half million Euros for a boy, 750 if it's a girl. Frau Pech points out that they can get more for it on the open market, but Adalind says that what she wants are her powers restored. Stefania warns her that it may not be possible and Adalind threatens to abort the child. Frau Pech advises her to take the money but Adalind stands firm.
Back at the station, Nick and Renard go over Marcus' record. He used to be an archaeologist and has been arrested numerous times for assault and property damage. Marcus disappeared 15 years ago when he began his crimes, and his wife died the same way as Jill. Nick figures that Marcus is involved with Jill's death, but admits that he didn't recognize the man's Wesen identity. Renard offers to help and Nick reluctantly agrees.
Juliette returns home and the memories start again. She goes outside and reviews Pilar's instructions, and sees another Nick-memory coming up with some boxes. Juliette tries to remember what she did and repeats the words she said on the day he moved in with her. Together they replay the day and how they both asked the other if they had second thoughts.
Nick and Renard tell Marcus that they know what he really is. Marcus insists that he was trying to warn Jill that she was taking "his" property, and says that they don't know what he is. The Wesen says that the creature he's trying to stop from rising is Volcanalis and he wants his revenge. Nick asks about Marcus' wife and the former archaeologist says that he couldn't save her, either. The two officers step out and Renard points out that in mythology, Volcanalis was a priest of Vulcan, the Roman God of Fire. Nick wonders if they're dealing with a fiery Wesen and they both agree to handle it off the books. As Wu comes in, the building shakes from a tremor. Once it stops, the sergeant tells them that there have been several attacks on people who took rocks from volcano sites on the Ring of Fire surrounding the Pacific. According to legend, the theft of sacred stones results in death. Once Wu leaves, Nick remembers that Thom took some rocks and they head out to visit him.
That night, Thom is at home eating supper when he hears something outside. Assuming it's his wife, home earlier, Thom checks but doesn't see anyone. When he goes back to the kitchen, he discovers that the rocks he was studying are gone. The water in a coffee pot starts boiling, the lights go out, and the fiery creature grabs Thom. Nick and Renard arrive and tell Volcanalis to drop his victim. The Wesen casually tosses Thom away and they open fire, but the bullets have no effect. Volcanalis walks out past them and by the time Nick and Renard recover from the heat and smoke, the Wesen has made its escape. Nick chases after him but he escapes into the sewers.
Juliette continues to relive the memories of the day that Nick moved in with her. She goes to get him a beer and realizes the refrigerator is now full, and comes back to reality. Looking around, Juliette realizes that she isn't haunted by memories of Nick.
At Marie's trailer, Nick and Eddie go through the journals. Nick finds a reference to the Taureus-Armenta, which describes the Wesen as stubborn and courageous. Monroe finds an entry on Volcanalis but it's in Latin. They take it to Renard to translate, and he reads bout how many of the people of Pompeii took rocks from the volcano. They all turned up dead, charred almost beyond recognition, and the Grimm escaped just as Vesuvius erupted. They wonder if Volcanalis had anything to do with Mt. St. Helens, and Nick suggests that they consult with Marcus.
Nick and Renard show Marcus the sketches of Volcanalis and he immediately confirms that it's the Wesen at Mt. Hood. They plan to pick up more of the rocks and lure Volcanalis out, and want Marcus to come with them. He doesn't know where Volcanalis can be found or how it finds its victims, and there's nothing they can do against the creature. Renard asks if he wants to get revenge on his wife's killer, and Marcus vows to die if he can take Volcanalis with him. Nick gets an idea and asks how cold they can make it.
Nick, Renard, Eddie, and Marcus go to the fumarole and take the rocks closest to the vent. They drive back down the mountain, towing a flatbed holding a covered device, and go to a sheet metal company. Inside, the group puts the rocks in the middle of the factory and then set up their cargo: three tanks of liquid nitrogen. Marcus stands near the rocks, acting as bait, while the others prepare to spray Volcanalis when he arrives.
The temperature in the factory starts to rise and the floor shakes. A nearby manhole cover turns red-hot and then explodes upward, and Volcanalis emerges. Marcus dares it to come after him and once it's in position, the others spray it with liquid nitrogen. The Wesen freezes solid and Nick offers an axe handle to Marcus. The Wesen takes it and smashes Volcanalis apart. They look at the pieces and the creature's eye look up at them for a moment before fading away.
Juliette opens up her drawer and puts up all of the photos of her and Nick that she's hid away since her coma. She finds the engagement ring that Nick gave her, contemplates it, and then goes downstairs to the couch. Concentrating, Juliette remembers when Nick proposed to her and smiles.