The Wolf thought to himself, what a tender young creature. What a nice plump mouthful... The Brothers Grimm, 1812
In Portland, college co-ed Sylvie Oster leaves her dorm room and goes jogging in the nearby forest park, wearing a red sweatshirt and carrying an iPod playing the Eurythmics' "Sweet Dreams." She notices a Hummel figure on a log and examines it... and a creature leaps from the woods and attacks her.
Detective Nick Burkhardt is picking up an engagement ring for his fiancée while his partner, Hank Griffin, takes photos with the camera. Nick notices a young businesswoman, Adelind Engel, but insists to Hank that he's only interested in her because of the deductions he can make about her. As she walks away, Nick sees her face change into that of a monster, but no one else notices anything unusual.
A hiker finds Sylvie's dismembered corpse in the forest and the police are called in. Hank and Nick talk to the forest service officer, who explains what happened and admits they could only identified the dismembered limbs by the woman's red sweater and pink Nikes. Nick and Hank find the iPod, still playing "Sweet Dreams," and then locate a boot print. As they head back to the station, Nick points out that a similar dismemberment murder took place a month ago but there were no boot prints. As he goes to his desk to check for reported predators, Nick sees a suspect whose face changes into that of a monster, but again, no one else notices anything.
An elderly woman, suffering hair loss from chemotherapy, drives her truck and trailer up to Nick's house and looks in the window.
Nick has no luck with the police database, but Hank tells him they have a report on a missing college co-ed. They go to the college and talk to Sylvie's roommate, who gives them a photo of Sylvie and confirms she was wearing the pink Nikes. The two officers return to the station and confirm that Sylvie was the victim. As they leave for the night, Nick almost leaves the engagement ring behind and Hank gives it back to him, telling him not to blow it. Nick heads home and calls out to his fiancée, Juliette Silverton, but gets no response. He goes into the kitchen and finds the woman, Marie Kessler, seated at the dinner table. He greets her and Juliette says that Nick's aunt arrived before she got home. As Marie and Nick hug, she tells him that they need to talk privately.
Nick and Marie go for a stroll and she explains that she has cancer but the doctors can't tell how long she has. She tells Nick that she couldn't come any sooner and that there are things he needs to know about her family. Marie confirms that he's been seeing monstrous faces recently and explains that the family curse has passed onto Nick. As she tells him to leave Juliette, Marie sees a man in a parked car nearby. She tells Nick that Hulda is there and draws a hidden knife from her cane. Hulda, a humanoid beast, leaps out of the bushes and attacks her with a scythe. Marie manages to fend him off with her weapon, but Hulda injures her and Nick manages to shoot him down just in time. As he lies dying, Hulda transforms back into a normal human form. Nick goes to Marie, who apologizes for leading the creature to him, and warns that they're after her and now him. She gives him a necklace with an amulet on it and tells him not to lose it, and then mutters that Nick's parents didn't die in a car crash before she passes out.
The police arrive and secure the crime scene, and Nick tells Hank what happened. Hank tells his partner to go to the hospital while they take care of the crime scene, and Nick waits there. He makes a sketch of the bestial Hulda and then Dr. Rose calls him in to see Marie. Once they're alone, she tells him that their family has the ability to see monsters no matter how they hide when they lose control, and that all the creatures from fairy tales are real. Marie tells Nick that he is one of the last Grimms, and that everything he needs for his new "job" is in her trailer.
Nick leaves the hospital and examines the amulet, and discovers that it holds a key. At the station, he check son Hulda's scythe and translates the words on the blade as "Reapers of the Grimms." Hank informs his partner that Hulda's fingerprints have turned up at rapes and murders across the country. As Nick leaves for the night, Captain Renard approaches him and asks how he's doing. Nick assures him that he's fine but Renard insists that he'll need to see a police psychologist, part of the standard procedure after a shooting.
That night, Nick has a nightmare of Juliette running through a forest, trying to escape Hulda. When he wakes up, he goes to Marie's trailer and finds a room filled with herbs and roots, a closet of medieval weaponry, and several books with sketches and photos of various creatures. Juliette comes in, startling him, and he takes her back to the house. As they go inside, Nick explains that Marie was like a mother to him after his parents died, but she didn't have the trailer when he lived with her. Meanwhile, something watches them from the trees.
The next day, Nick checks the DNA from the boot print but is unable to identify the killer from it. Hank has located an advertisement featuring the boot with the boot print, a fairly exclusive brand.
A postman wearing the boots is dropping off mail in a neighborhood when he sees a young girl wearing a red hooded sweatshirt and purple leggings. He turns around and follows her down the street.
The next day, Nick checks on Marie and Dr. Rose informs him that his aunt has gone into coma. She points out that Marie's body is covered in old knife wounds and Nick admits that he thought she was a library. Hank calls Nick to the house where the young girl, Robin Howell, has been reported missing by her mother and grandfather. Robin was on her way to her grandfather's house but never made it. Back at the station, Renard coordinates a task force to find the girl. Nick notices that Robin was wearing a red sweatshirt when she was abducted, and that Sylvie was wearing a red sweatshirt when she was murdered.
Hank and Nick return to the neighborhood and trace Robin's path to her grandfather's house. It goes by a park, and Hank figures that Robin would have gone through it despite her mother's instructions to the contrary. The partners split up and Hank finds Robin's backpack, while Nick finds more boot prints matching the previous one. He follows the trail out of the park and sees a man across the street getting his mail. As two young girls ride by, the man's face briefly turns wolf-like. Nick runs down the hill and goes into the house after the man, throws him to the floor, and demands to know where he's hidden Robin. Hank and the other officers, including Sgt. Wu, search the house but find no sign of Robin. Hank warns his partner that they have no evidence against the man, Eddy Munroe, and Nick can't explain what he saw.
That night, Nick goes back to Marie's trailer and goes through her books while Juliette watches from the bedroom window. Nick finds a sketch of the wolf-creature that he saw and goes back to Eddy's house. Juliette calls him but Nick ignores the call and watches as Eddy goes behind the house and urinates on the fence. Eddy then goes into the house and Nick starts to sneak around the back, but Eddy leaps out the window in his beast form and attacks Nick, slamming him into the wall. He then invites Nick inside for a beer.
In the house, Eddy explains that his parents used to scare him with stories of the Grimms, monster hunters. When Nick mentions Marie, Eddy admits that he's heard of her but that Nick seems kind of new to the business. He explains that he's a blutbad, a name that humans have vulgarized as "big bad wolf," but that he is no longer bad. When Nick wonders if he can stop seeing the faces, Eddy warns him that there's no way to go back to normal. Nick figures that another of Eddy's kind abducted Robin and asks for his help, but Eddy refuses to become involved until Nick reminds Eddy that he's a cop and that her life is at stake.
The postman drives out to his isolated cabin in the wood. He takes Robin inside and down through a hidden trapdoor to the cellar. There is an elaborate bed and the postman sets her down, telling her that the cellar is her new home. He puts her red sweater in a close with several others and then offers to make her a chicken pot pie.
Eddy gives in and drives through the forest, following the other blutbad's scent while Nick nervously rides shotgun. As he drives, Eddy explains that the blutbad will fatten up Robin for a week or so and then eat her. They pull over and Eddy puts wolfsbane on himself and Nick to cover their scent. They then go through a stream and approach the blutbad's home via the back way. However, Eddy starts to transform and he warns Nick that the closer he gets to another of his kind, the more likely he will go berserk. He tells Nick that he's on his own and runs away, and Nick calls Hank for backup.
Inside the cabin, the postman smells something on the wind but isn't sure what. He's distracted when Robin knocks on the trapdoor and asks him to let her go home. The postman tells her again that she is home and locks her in.
Hank arrives and is surprised when Nick puts some wolfsbane on him. Nick explains that Hank was the only one he could call because the other officers would think he was crying wolf. They go the back away and Nick tries to explain how he found the postman. As they approach the cabin, Nick asks Hank if he trusts him despite his reservations, and Hank says that they need to do it. They knock on the door and the postman invites him in. He isn't wearing the boots and wonders why they suspect him. When Nick accuses him of murder and abduction, the postman invites them to look around for the boots while he hums a song and makes chicken pot pie. The officers find nothing and Hank tells his partner that they have to leave because of the lack of evidence.
As they go back to the car, Hank realizes that the postman was humming "Sweet Dreams," the same song from the dead girl's iPod. They break into the cabin and discover that the postman has turned off the lights. They search the cabin and the postman, in his wolf form, attacks them. He knocks them both to the floor and runs out, but Hank manages to shoot him in the back, bringing him down. The postman transforms back into human form and Nick runs over and asks where he's hidden Robin. The blutbad mutters "Grimm" and dies. As Hank calls for backup, Nick goes back into the cabin and notices that the water from a broken vase isn't pooling on the floor. He finds the trapdoor and rescues Robin, assuring her that she'll be okay.
Later, Nick goes back to the hospital to see the comatose Marie. He tells her that he'll do what it has to, but doesn't want to lose Juliette. A doctor comes in and prepares to give Marie an injection, but Nick realizes that it's Adelind, the disguised creature he saw earlier. He tries to stop her and Adelind injects him with the syringe meant for Marie, and then runs out as Nick collapses. She goes out the employee entrance and gets into a car with... Captain Renard. Adelind admits that Nick stopped her from killing Marie, and Renard tells her that they have to kill Marie before she wakes up. Meanwhile, in the hospital room, the doctors tend to Nick while Marie opens her eyes.