Young, rowdy couple Gilda and Rocky break into a large, grand home in the middle of the woods. Up to no good, they're clearly drunk and looking for trouble. The two raid the fridge and the liquor cabinet and play the part of the rich out-of-town residents, jokingly adorning their expensive clothes.
The couple makes their way to the bedroom, only to hear someone arrive home downstairs. They try to make an escape, as Gilda jumps out of the second-story window first. Unfortunately, Rocky isn't as quick, and gets caught and attacked by whoever entered the house. Gilda listens on as Rocky's screams and an animal growl comes from the house, realizing that it's too late for Rocky to make an escape from whatever has captured him. Gilda jumps into Rocky's truck and takes off into the woods.
Meanwhile, detective Nick Burkhart is still recuperating from the attack he suffered at the hospital, which was intended for Aunt Marie. After reviewing the security tapes for his attacker, all they can find is a blonde woman from the back; it's going to be difficult to identify her. While Nick's fully aware of the Grimm creatures' intentions, Nick's partner Hank wonders what Aunt Marie did to get so many enemies out for blood.
The news comes in about a DUI, and the driver has some crazy story about her boyfriend being attacked. Nick and Hank question Gilda to see if there's something more to her story. They decide to investigate and arrive at the house where the supposed attack happened to question the residents.
Mr. and Mrs. Rabe report that someone broke into their house, but they know nothing of the attack on the intruder. It all seems like a pretty standard breaking and entering, until Nick notes their rather interesting artifact collection, including a carved fierce bear head on a claw-like weapon, apparently of ancient Germanic origin. For Nick, there's something very familiar about this particular weapon...
Meanwhile, poor Rocky is bound and blindfolded and scared out of his wits. As it turns out, Gilda's story about her boyfriend being attacked wasn't a drunken hallucination after all. A face suddenly appears from darkness, right next to Rocky's face... it's not human, but it's not quite a bear either.
Aunt Marie comes to; she's extremely weak but has pertinent information for Nick. She tells him that his ability is a responsibility he can't ignore. He has to hunt down the bad ones, just like his ancestors did, and take on his roll as a Grimm.
Nick and Hank go back to the Rabe home for further questioning and happen to run into their 18-year-old son, Barry, and his two friends. The family insists that Barry was staying with friends the night of the kidnapping and was nowhere near the house, but their overly defensive nature arouses suspicion. When Nick sees the boy briefly morph into a bear-like creature, he knows that they're definitely up to no good. Hank gets a bad vibe as well; the two decide to trace Barry's calls and figure out exactly where the family was that night.
That night, Nick has a dream where he and his aunt are in her trailer. She warns him of the coming danger and then stabs Nick in the hand with a knife she uncovers from the weapons cabinet. Nick wakes, startled; what could this possibly mean? Nick goes into the trailer to mull over this nightmare and comes across a bear claw weapon very similar to the one discovered at the Rabe's home; the pieces of this puzzle are starting to fall together.
The next morning, Nick pays a visit to Monroe to further investigate the significance of the bear claw. Monroe, upset that Nick interrupted his morning Pilates session, explains that the weapon belongs to Jagerbars and is typically used for disemboweling. The claw is used for the Roh-Hatz, a special coming-of-age ceremony for the transformation of a young Jagerbar from boy to man. Monroe claims the ceremony is a bloody one, and it's "all about the chase." It seems that a connection between young Barry and the missing Rocky is becoming more and more apparent.
Nick gets a phone call from Hank; Gilda made bail and apparently is on a mission to confront the family and demand to know Rocky's location. At the scene, Gilda's arrived and is met with a brutal attack by Barry, leaving her unconscious. The mother is apparently in on the scheme, telling her son that hunting two is better than one. Barry takes off with his new captive, but when the father arrives home, it's made apparent that he's been left in the dark.
Meanwhile, Monroe has begrudgingly agreed to keep watch over Aunt Marie at the hospital for Nick. Monroe has a hard time rationalizing cooperating with a woman who murdered his ancestors, but eventually he pulls through for Nick. It turns out his help was definitely needed; Monroe fends off two attackers, and things go a little too far when he accidentally rips a man's arm off with his Blutbad super-strength. Whoops.
When Nick arrives at the home of the Rabes and confesses that he knows what's going on, the husband Frank realizes that his wife and son have been lying to him all along. Frank agrees to help Nick and takes him into the forest to find Rocky and Gilda before it's too late. When they find an empty cave with some of Rocky and Gilda's clothes on the floor, they fear that it may be too late.
Meanwhile, the hunt is on, as Rocky and Gilda running for their lives. Behind them, Barry and his two friends are fully morphed, growling, howling and relishing the chase. Each carries the claw weapon; things aren't looking so good for Rocky and Gilda.
Nick and Frank finally catch up with the boys who have their two victims trapped, loving the chase too much to let it end so soon. Frank demands that it stop now, but Barry is riled up and ready to take down Nick if he has to.
Barry breaks free from his dad and shoves him aside, heading for Nick, who is about to shoot when he hears a roaring growl from behind. Nick spins to see a fully morphed female Jagerbar coming at him. But before Nick can fire, she disappears into the earth, into the hidden stake pit dug by the boys. They move to the edge of the pit, where Barry's mother un-morphs, severely injured.
The cops arrive to clean up the scene and arrest the boys, when Nick gets a call from Monroe back at the hospital. He explains that he did his job but can't stick around; things are getting dicey. Nick arrives at the hospital to find Marie in a fight with a man dressed as a priest; yet another attack by the reapers of the Grimms. While Marie wins the fight, it took all the strength she had left. Marie dies in Nick's arms, telling him to remember who he is - to trust his instincts and nothing else.