Said the dragon, “Many knights have left their lives here. I shall soon have an end to you, too,” and he breathed fire out of seven jaws.

Two men, Joe and Stu Oliver, pull up to an abandoned supply house to scavenge for copper and discover that someone has already cut through the chain on the gate. They go inside and go to a particular door, and discover that the handle is hot. The men continue and hear someone moving around inside and see a flash of fire, and yell telling their rival to take off. Someone sprays liquid on them and then a vast burst of flame fills the room, killing them. A reptilian creature looks on in satisfaction.

Outside, a man is driving by and almost hits another man with scarred features he runs across the street. Soon the man is making off on a railroad cart into the hills outside of Portland.

The next day, Nick and Hank arrive at the warehouse. A pickup is outside and Wu has confirmed it belongs to Joe Oliver, a small-time thief. Lance Truman, the owner of the building, is waiting to talk to them. He found the bodies and called it in, and is currently waiting to talk to them. The officers go to the basement and meet with the arson investigator, Jordan Vance. He’s puzzled about how the two men were burned in an explosion when there’s no obvious accelerant. Whatever it was got very hot very fast. Outside Truman tells them that he’s secured all of his buildings but people still keep breaking in. The lock on the door was also burned out by something with incredible heat. As they talk, Hank notices a small puddle of oil and sets it on fire, and it goes off in a quick burst.

At the station, Vance tells Renard that the substance is lipid: human fat, which burns incredibly hot and fast. He doesn’t know where someone would find that much human fat. Nick and Hank think that it’s homicide and that there have been similar thefts. Whoever is stealing the copper isn’t selling it. The driver comes in and reports that he saw someone run past him and gives a description, and suggests the man was homeless. The detectives have him sit down with a sketch artist so they can get a description.

At the warehouse, Truman is locking up the gate when the suspect comes up and knocks him out.

Nick and Hank are working with the sketch artist when Wu comes in and reports that Truman has been attacked. The two officers arrive and go in with Wu and several other officers. Wu hears something near the loading dock and goes to investigate, but is sprayed with something and can’t breathe. Nick tells him over the radio to back away without firing his gun. They arrive and find the suspect, who sprays more of the lipid at them from his mouth. As Hank falls back, Nick sees that the man is a reptilian creature. He breathes fire from his mouth and escapes in the confusion, running outside, grabbing his bag of copper, and escaping on his railroad cart.

Hank and Nick check on Wu, who is in bad condition. Back at the station, Vance tells them that they have a DNA match on the lipids. The suspect is Fred Eberhart, age 48, who has been in and out of VA hospitals and disappeared six months ago. Eberhart was previously working as a welder on a railroad and was laid off two years ago. His only relative is his daughter, Ariel, and Nick calls her while Hank admits to Renard that he heard a coughing noise right before Eberhart attacked them. Meanwhile, Nick gets answering machine on the number for Club Trop Chaud and says that he’ll check it out on the way home.

Nick stops at the club and asks the hostess to see Ariel. She shows Nick Ariel… performing a fire-dancing routine. He realizes that there re are several creatures in the audience, including Monroe. As he approaches the stage, Ariel blows some fire and he sees her as a creature as well, the same type as the one he saw at the supply house. Nick sits down with Monroe, who admits that he comes there a lot to see Ariel. The detective explains that he’s there about Fred and Monroe explains that Ariel and Fred are daemonfeuers, and nervously wonders if they should be seen together in public. They go outside and Monroe explains that daemonfeuers are rare and come from a dragon-like lineage. He confirms that they can breathe fire by burning their own fat, which is highly explosive. Before he leaves, Monroe tells Nick that he got a report form a cousin in Germany that a Grimm was decapitated and his head hasn’t been found.

Nick goes back into the club to see Ariel in her dressing room. She invites him in and he explains that he’s there on a fire-related homicide. Ariel undresses and tells him that he’s her first Grimm, but not exactly what she expected. She tells him that Grimms are reputed to be tough and she finds the stories a turn-on. Nick focuses on the case and asks about Fred, and Ariel tells him that she doesn’t know where her father is. She explains that after her mother died, Fred fell apart because he couldn’t protect her and drifted away. Ariel doesn’t know any way to contact him and wonders if Fred was really the killer, and Nick says that he wants to stop him before he hurts someone else. He gives Ariel his card and leaves.

Later that night, Ariel goes to her car. Nick is watching her and follows in his car as she drives home. As she goes inside, Nick checks the house and discovers that there are a dozen lightning rods on the roof. There is a roaring noise and a burst of flame from the backyard and Nick circles around to the back. Ariel tackles him, rips open his shirt, and then kisses him. Nick throws her off as she laughs, and Ariel explains that she was doing a little purging. Juliette calls and Ariel answers the phone, claiming that she’s with Nick. Nick tries to grab the phone and explain but Juliette angrily hangs up. As he walks away, Ariel calls out that he came for her.

Back at home, Nick tries to explain and says that Ariel is crazy. She isn’t convinced when Nick says that he is trying to help find her dad, and that Ariel is a fire-dancer. Nick apologizes and assures Juliette that he wouldn’t do anything like that to her, and she kisses him. Outside, Ariel sprays lipids on the window and draws a heart in the liquid fat.

Nick goes to Marie’s trailer and reads an account on a Grimm hunting a daemonfeuer. It talks about an entrance to Hell.

Ariel goes into the hills and enters the mine that Fred uses as a lair. Her father is there, unconscious, and Ariel tells him that she’s found someone who is going to make him better.

The next morning, Nick and Hank talk to Fred’s previous employer. As they walk along the tracks, the man explains that Fred’s wife died in a fire and Fred just stopped showing up for work. The last time he saw Fred, the man was walking down the tracks on an old mining spur. Back at the station, Nick finds a map of the old rail lines and locates the spur line that goes up into the hills. He figures that the mines would make a great lair. Ariel calls Nick and teasingly invites him to a special show, and then says that she’s decided to help him find her dad and asks him to stop by her house that night. Once he hangs up, Nick tells Hank what Ariel said and that he wants Hank with him. He then calls Juliette to tell her what’s going on and Hank assures her that he’ll be there with his partner.

That night, the detectives go to Ariel’s house but she doesn’t answer the door. They wonder if Fred found out she was going to help them and came after his own daughter. They break in and find the house covered in copper decorations, utensils, and wiring. There are photos of her relatives, who all served in the military and used flamethrowers. The two men hear thunder and quickly get out, and Hank tells Nick to go home and get some… rest while he puts out an APB.

When Nick gets home, he goes to the bedroom and finds Ariel in his bed. She’s waiting for him and tells Nick that he has her now. He shoves her against the wall and she breathes out flames, giving herself time to escape. The phone rings and Nick answers it: it’s Ariel, who tells him that it’s time for him to rescue his girlfriend. She explains that Nick will have to face her father alone, and he knows where to find him.

Nick collects Monroe, who goes over the maps and figures out which tunnel that Ariel is using. He explains that she has set up a cal quest, but the problem is that someone always dies.

Ariel puts Juliette on the cart and takes it into the mines.

Nick and Monroe arrive and find Juliette’s car. They find a section car and Monroe knows how to run it, and they head into the tunnels.

Ariel arrives at her father’s lair and takes Juliette inside past the walls covered in copper. She wakes Fred up and says that Juliette is there and she’s just like his wife, and now it’s his chance. Fred walks over to where Juliette is tied up and asks who is coming for her, and Ariel assures him that it’s someone worthy of her.

The two men stop the section car outside of the mine and go in on foot. Monroe wonders what they’re going to do and Nick says that he’s giving them what they want. He tells Monroe to get to Juliette while he distracts them. Nick grabs a pipe to use as a weapon and calls out for Ariel. Meanwhile, Monroe moves off and sees several tanks of acetylene gas. Ariel hears Nick and tells her deluded father to protect his wife, since he thinks that Juliette is his wife.

Monroe finds Juliette and unties her, but hears someone approaching and quickly hides. Ariel comes over and removes Juliette’s gag. Juliette punches her and runs off with Monroe.

Fred confronts Nick, breathing fire, and Nick attacks him once the flames die down. The daemonfeuer disarms him and unleashes another burst of fire. When he pauses to recover, Nick lunges at him and the two men struggle. Before Fred can fire another blast, Nick impales him with a pipe. Ariel arrives just in time to see her father go down. She tells him that he fought valiantly as he passes away. She then thanks Nick for letting her father die with dignity. She tells Nick that it’s her turn, spews lips everywhere, and unleashes a burst of flame. He gets out just in time to where Juliette and Monroe are waiting. While Nick calls in the police, Monroe explains to Juliette that he’s a private investigator and it’s nice to meet her.

Later, Nick drives Juliette home and she asks him to pull over. Once they stop, Juliette tells him that Ariel was crazy and he couldn’t have known what she was going to do. However, she warns that she can’t keep living with a cop if it puts her in danger. Nick remembers Marie telling him to end his relationship with Juliette, and asks his fiancée what she wants to do. Juliette says that she’s too tired to discuss it now and says that she’s glad the bitch is dead.

Ariel emerges from the mine, singed but unharmed.