The Demon came home and he declared that the air was not clear. “I smell the flesh of man.”

Geologist Jill Prembrey with Eon Industries is checking out active fumaroles on Mt. Hood. As she takes a video recording of her finds, she hears someone moving in the woods. When they don’t reveal themselves, Jill goes back to her truck and prepares to leave. A man, Marcus Hemming, grabs her rocks and yells that they don’t belong to her. Jill hits him with pepper spray, grabs the pack of rocks, and drives away. As she calls her boss and tells him what happened, Marcus glares after her and transforms into a bull-like Wesen.

At the station, Nick and Wu finally harass Hank into taking his first vacation in four years. Renard comes over and orders Hank to get going, and they wheel him to the door for his three-week vacation.

Juliette nervously returns home and makes her way to the kitchen with her groceries. As she starts to put them away, images of Nick appear in her mind, reliving moments from their past together, and Juliette screams at them to stop. She runs out past another image of Nick, gets in her car, and drives away. Another image of Nick appears in the passenger seat and when she tries to hit it, she loses control of the car and rams into a parked vehicle.

In Vienna, Adalind is going through morning sickness when Frau Pech arrives and tells Adalind that they have a meeting with the Zigeunersprache: the queen of the Schwarzwald Gypsies. Adalind isn’t interested but Frau Pech warns her that she’s gone to a great deal of effort to establish a meeting, and that the true value of motherhood is finding out how much Adalind’s child is worth.

Nick goes to the hospital to see Juliette, who has a mild concussion. Once she makes sure he’s not another memory-image, Juliette tells him that because of what they did to her at the spice shop, she sees Nick everywhere. He doesn’t understand what she means but Juliette insists that she can’t see him anymore and orders him out.

When Jill gets home that night, there’s a brief tremor that shakes her house. She hears something burning in the dining room and finds all of the plastic melting. As the wallpaper starts to char, a fiery humanoid figure lunges out of the next room and attacks her.

Nick, Monroe, and Bud are at Bud’s place watching soccer, but Nick isn’t paying any attention because he’s dwelling on his problems with Juliette. The two Wesen offer their sympathies and say that they’ve all been there, but Nick decides to call it a night. As he heads out, he gets a call from Wu tell him about Jill’s murder and heads there to investigate.

Juliette goes to see Pilar, who can sense that the younger woman’s memory issues are getting worse.

When Nick arrives at Jill’s house, Wu informs him that a co-worker called in when Jill didn’t show up for a dinner date. They check Jill’s body and discover hand-shaped burn marks charred into her face and neck. Everything in the house has been exposed to extreme heat but there are no signs of fire. Wu finds Jill’s camera and they play back the Mt. Hood video, confirming where she was that day.

Pilar gives Juliette a drug to help her focus and explains that Juliette’s missing memories are returning. However, they are all returning at once and Juliette has to select one particular memory and immerse herself completely into it. If Juliette doesn’t go home and embrace a memory, she has no future.

Frau Pech takes Adalind to the Gypsy camp and brings her to Stefania Veduva Popescu, the camp’s queen. Stefania takes them into her tent where her two sons are waiting, and explains that there is only one way to be sure of the child’s bloodline. Her two sons hold Adalind down while Stefania takes out a huge syringe and prepares to remove some blood.

The next day, Nick and Wu visit Eon and talk with Jill’s boss, Thom Evans. He gives them the location where she was working and tells them about the attack that she reported. Nick confirms that Jill was taking rock samples and Thom drives the two officers to the site to investigate. As they check it out, Thom admits that they’ve had problems with eco-protestors but nothing major. The vent is still active and Thom warns Nick and Wu that the nearby volcano is becoming active.

As they talk, Nick sense something on the edge of his senses but can’t get a fix on it. Thom pockets a few rocks from the fumarole and they go back to his truck, only to discover that someone has smashed in the windows. Nick hears someone moving and chases after him, and finds Marcus. The Wesen woges into his bull-form and runs off, and Nick chases him. Wu manages to tackle the Wesen, who is back in his human form, and they handcuff him. As they secure him, Marcus screams that they’re all going to die because they didn’t show respect.

Stefania conducts the blood test and tells Adalind that she was telling the truth when she claimed the child had Royal blood. The gypsy offers money for the child, more if it’s a boy, but Frau Pech is unimpressed and tries to negotiate. Adalind says that she doesn’t want money: her price is her powers, restored. Stefania warns her that it may not be possible and Adalind threatens to abort the child if she can’t meet her conditions.

Back at the station, Nick informs Renard that they’re dealing with a Wesen and check Marcus’ history. An archaeologist, Marcus disappeared 15 years ago when his wife was murdered in the same way that Jill was. Since then he’s been arrested several times for assault and property damage. Nick figures that they have to identify what kind of Wesen that Marcus is, and reluctantly accepts Renard’s offer of help.

Juliette goes home and is soon experiencing memories again. She steps outside and tries to focus, and sees a memory-image of Nick bringing in his belongings as he moves in with her. She repeats the words that she said on that day, merging with the memory, and they talk about whether either one of them is having second thoughts.

Nick and Renard tell Marcus that they know he’s a Wesen. Marcus says that he didn’t kill Jill and was trying to warn her against the creature that did: Volcanalis. The former archaeologist tells them that the same Wesen killed his wife 15 years ago and now he wants revenge. When the two men can talk privately in Renard’s office, they decide to handle the case off the books. Wu comes in to tell them that he’s checked the records and confirmed that there have been several similar attacks near volcanos on the Pacific Rim, the “Ring of Fire.” In each case the victim took supposedly sacred stones from a volcano site. Once Wu leaves, Nick remembers that Thom took some rocks from the fumarole and the two men head out to check it out.

Thom is at home eating supper because his wife is working late, and studying the rocks from the fumarole. He hears someone outside and checks it out, but doesn’t see anyone. When he comes back, the rocks are gone and the water in a pot is boiling by itself. The lights go out and Volcanalis grabs Thom. Nick and Renard break in and order the Wesen to surrender. The creature tosses Thom’s corpse aside and runs for the door, and the two officers open fire. Their bullets melt before they can hit the Wesen, and the heat and smoke overwhelm the men. By the time they recover, Volcanalis has escaped via a sewer grate.

As Juliette continues to relive the memories, she finally goes to the refrigerator to get “nick” a bear. When she sees that it’s now full, she snaps out of her spell and looks around nervously. However, no more images of Nick appear.

Nick and Monroe go to Marie’s trailer to check her journals and Nick finds a reference to a Wesen known as a Taureus-Armenta, which matches Marcus’ description. The Monroe finds an entry on Volcanalis but the entry is in Latin. They go to the station and have Renard translate it, and he explains that the Grimm encountered Volcanalis in Pompeii when many of the residents took the sacred stones. They were all killed, charred to death, and the Grimm escaped as Volcanalis caused Vesuvius to erupt.

Nick and Renard meet with Marcus, who confirms the sketches are of Volcanalis. They tell Marcus that they plan to lure Volcanalis to them by taking the rocks and want Marcus’ help. He insists that he doesn’t know anything about the creature or how they can find it but Renard offers him the chance to get revenge for his dead wife. Marcus promises to destroy Volcanalis even if he dies, and Neck asks how cold they can make it.

Nick and the others go to the fumarole and take some of the rocks, and then drive to a sheet metal factory. They put the rocks in the center of the main room and then set up three cylinders of liquid nitrogen around the perimeter. Marcus acts as bait, standing next to the rocks, while the others wait for Volcanalis to arrive. The temperature starts rising and the floor shakes, and a nearby manhole cover explodes upwards in a burst of heat. Volcanalis climbs up and advances on Marcus, who dares it to come after him. The others spray it with liquid nitrogen and the Wesen freezes solid except for its eyes, which can still move. Nick gives an axe handle to Marcus, who smashes his wife’s killer to pieces. An eye looks up from one piece for a moment before fading away as the creature dies for good.

Juliette takes out all of her photos of her and Nick together, photos that she put away after she woke up from her coma. She also finds the engagement ring that Nick gave her and goes downstairs to the couch. Juliette puts it down and concentrates, and remembers Nick proposing to her.