A young college student in pink sneakers and a bright red sweatshirt heads out for a morning jog through the woods. She's got "Sweet Dreams" playing on her iPod, and the only thing she may be worried about is the mud on her feet. On the trail, she stops to look at a small figurine that sits atop a mossy log. WHAM! Out of nowhere something superhuman snatches her from her tracks. All that's left is her screaming. She's silenced by the growls of this wild beast as it tears her limb from limb.
Hank Griffin snaps a photo of his partner, Nick Burckhardt, as he exits a jewelry shop with an engagement ring. A pretty woman catches Nick's eye, but it's not because she has a pretty face. Well, she does have a pretty face until it morphs into that of a monster for a brief moment. He shakes it off.
Nick and Hank explore the woods where the college student was attacked. There's a bloody limb behind a bush, and the rest of the remains are scattered around. There's only one footprint... and it's not an animal. Our superhuman creature seems to be human. Nick and Hank pursue the case back at the office where Nick spots another human-morphed-monster. Now, he's really freaked out.
At the office, Hank gets a lead. He and Nick speak with a concerned student who tells them that her friend went out jogging this morning and never came back. She was wearing pink sneakers... there were pink sneakers at the crime scene. Sylvie Oster is her name.
Nick is met at home by his girlfriend, Juliette, and a surprise visit from his Aunt Marie. Aunt Marie pulls Nick aside to discuss a serious issue; this is no fun visit. There's something different about Nick's family; something hard to explain. Before Marie can get any further, a monster jumps out from the bushes and attacks! Marie fights him off, but it's not enough. Just as she's about to lose, Nick shoots the monster dead. But, as he's breathing his last breaths, his face transforms into that of a normal human being. Nick killed a monster that somehow morphed back into a human... and again, Nick's left confused.
Nick rushes to his aunt's aid. Struggling to breathe, she rips a necklace off and gives it to Nick... to guard with his life. But before she passes out, she springs another surprise on Nick: his parents, who he believed died in a car accident, were actually murdered. Nick has a lot on his plate.
At the hospital, an unstable Aunt Marie reveals that Nick's family has the ability to see people for who they really are, and in this case, they're creatures from "Grimms' Fairy Tales." The fairy tales are true stories, and Nick is one of the last Grimms.
Nick inspects the monster's weapon from the crime scene. It is decorated with strange writing that spells out: "Reapers of the Grimms." To make him feel a little better, Hank tells Nick that the man he killed was a criminal on multiple accounts in multiple states. Nick's boss, Captain Renard, checks up on him.
Nick wakes up from a nightmare and goes outside to inspect Aunt Marie's trailer where she has hidden weapons, books and other Grimm equipment. Nick sifts through an open book that lays out the Grimm creatures. One of the first in the book matches the image of the pretty girl who morphed into a monster outside of the jewelry store.
The DNA of Sylvie Oster's attacker is still inconclusive. It could be a man... or a beast... or both. All the police know is that it was wearing a pair of boots. Back in town, a young girl in a red sweatshirt skips past a postman delivering mail in that same pair of boots. He stops in his tracks and deviously turns back to follow her.
Nick visits Aunt Marie at the hospital, who's fallen into a coma. The doctor asks Nick if he knows anything about the scars all over her body. The scars look like knife wounds, which comes as a surprise because Aunt Marie's a librarian. Nick gets a phone call for a missing persons case. After being followed by the postman, the little girl in the red-hooded sweatshirt went missing. Her nervous mother and grandfather watch as police search the area.
Nick and Hank explore the path that the missing girl may have traveled. Hank finds a little backpack with the initials R.H. on them... the same as the missing girl's. Nick finds bootprints like those from the first crime scene. He follows them to the edge of the woods where he sees a man in front of his house morph into a wolf. The wolf-man, realizing Nick saw his transformation, nervously heads back into his house, but not before Nick tackles him.
The missing girl is nowhere to be found, and the man Nick attacked gets released since there's no evidence. Nick later shows up at the wolf-man's house and is invited inside after they have another threatening altercation. He wants to talk to Nick. His name is Monroe, and he's interested in meeting a real Grimm like Nick up close and personal.
Monroe explains that there are many different Grimm creatures, but not all of them are villainous. Monroe has been able to quell his true nature and exist peacefully with humans, like many Grimm creatures do. Nick begins to understand, but now needs Monroe's help in finding the true identity of the man who kidnapped the young girl.
Meanwhile, the postman arrives at his eerie cabin in the woods and locks up the kidnapped girl in a basement bedroom after neatly hanging her red sweatshirt with his collection of others.
Nick and Monroe are on the postman's trail, as Monroe hangs his head out the window sniffing out danger. He picks up a scent and the two set off on foot. But when they get closer, Monroe morphs into his wolf-self, refusing to come any closer. He runs away, leaving Nick to fend for himself.
Nick calls his partner Hank with his location, and the two approach the house. Nick and Hank inspect the house of this seemingly harmless, sweet man, but they find nothing. But as they're walking away, Hank realizes that the postman was humming "Sweet Dreams," the same song that was playing on the first victim's iPod.
Nick and Hank storm the house. The postman, who has morphed into a wolf creature, jumps on Hank. He runs out of the house, but Hank fires before he can get away. Just as before, the creature turns into a human once he's killed, and Hank is left unaware of the creature's true identity. Nick and Hank go back inside and find the terrified young girl in the basement.
Nick goes to see Aunt Marie once more in the hospital. A doctor walks in to deliver an injection, but Nick is late to realize that it's the same woman he saw originally morph into a terrifying creature. Nick saves Aunt Marie from the injection at the last minute, taking the injection instead. He collapses, and the "doctor" makes a run for it.
A car picks up the woman, and the driver asks if she completed her mission. The driver turns out to be Captain Renard, who's apparently involved in the Grimm world as well. But the question is, why does he want Aunt Marie dead?