Nick Burkhardt, a promising Portland homicide detective, told nobody he gets visions of people 'transforming' into monsters when he looks at them. While investigating the murder and disappearance of two girls, he realizes it's a Grimm family gift, which passes from his aunt Marie Kessler when she is dying from cancer. She also gives him a mysterious key. Nick becomes her attacker's next target, but barely and wisely discretely uses his gift to track down the postman, who turns out a descendant of werewolf line, yet helps him find the violent monster.
Rocky Babb goes missing after breaking into lawyer Frank Rabe's desolate Forrest home with his girl-friend Gilda Darner, who escaped and urges the PPD to investigate. Nick believes her and Grimm-senses Frank's adolescent son Barry can change into a bear. Eddie Monroe Blutbad accepts grudgingly to guard aunt Marie Kessler in hospital while Nick and Hank check out Barry and his motorbike buddies, Jason and T.B. Colbert, who kidnapped Rocky for a grim sunset initiation hunt.
The station is abuzz as Nick and Hank are called to a case where an innocent flash mob results in a gruesome homicide. As Nick delves further into the investigation, he learns more about his unique family history, and finds himself at odds when he and Hank are assigned to protect a dark character from his recent past.
Nick discovers that several disappeared women were raped, a few also killed, after a stay in Billy Capra's romantic, honeymoon-oriented hotel. After a Grimm-flash shows him Bill as a goat, Nick enlists Eddie Monroe to help him identify the feral type, which uses irresistible seduction pheromones, and to prepare a hotel intrusion to save the latest victims. Meanwhile captain Sean Renard gives an uninvited French reaper a terrible welcome.
Nick and Hank's investigation of a dead high school teacher leads them to the school's outcast, Roddy. Nick realizes that there's more to Roddy than meets the eye, and enlists Monroe's help to get through to the troubled teenager before he exacts revenge on the students who wronged him. Meanwhile, Nick learns that his presence is beginning to affect the creature world.
Nick is called to a suspected arson case, which exposes a longstanding family feud that brings Monroe face-to-face with characters from his troubled past. While Monroe wrestles with restraining his wild side, it's up to Nick to keep everything from going up in flames.
A drug trafficker was murdered without apparent motive deep in the forest. Helped by unusually enthusiastic Monroe, Nick soon works out the killer must be a feral and after tracing her it's a girl. Then follows traces indicating she may be a long-missing child having nearly grown up in the woods, and suggesting a link with recluse tracker James Addison, but there are others involved.
Highly respected judge Logan Patterson is murdered, and shortly after several other people who played some part in the conviction and incarceration of an escaped giant of unnatural strength. Nick is badly wounded, out of action. Monroe however shows unusual enthusiasm to help out while Hank follows the paper trail.
While investigating a gruesome homicide, Nick learns that a seemingly mild-mannered resident could be festering a potential monster created from a dark childhood. Meanwhile, Monroe is sent an unsettling message by the creature community, who are beginning to wonder if his priorities lie with them or a Grimm.
A mysterious woman seduces men, then kills them in a way too gruesome to watch. Nick must uncover this new and rare creature's secret and find her before she kills again. Concurrently, Nick takes (admittedly belated) action to stop the (Wesen) creatures from rumor-mongering and stalking his home; in this show of power, Nick is slowly coming into his own as a Grimm - and defending house and home.
When Nick consults him about an erratic murder committed by athletic ex-con Dimitri Skontos, Monrie soon helps him realize that's actually a victim of 'gladiator games' organized by the most bloodthirsty pride of Löwen, a lionesque feral species. Nick spends his anniversary working out the fighters are recruited trough a dodgy parole officer and where the arena is hidden. Captain Sean Renard realizes the lucrative fights are becoming too notorious, his royal order to close down is ignored, so he turns to a priestly enforcer. Meanwhile first Monroe, then Nick co ...
Jeweler Sam Bertram was murdered by three Europeans killers, of rival feral species, to steal the rarest Ancient gold coins from his safe. Two are dead, the third steals a uniform from a cop he murders. The coins are found on the elusive Farley Kolt, who is arrested and tells Nick enough to work out he was late aunt Marie's true love. The coins, minted on Zakynthos, with swastika's and lions heads, are poisonous and magically attract great power and utter disaster. Captain Sean Renard keeps them and starts an ambitious 'campaign against crime' amidst dreams of ...
Nick is puzzled by several corpses with unusual semi-internal combustion symptoms. After Nick and hank are attacked by a fire-breathing dragon, which fits the riddle, Monroe teaches Nick about the suspect feral breed, not actual dragons but close, and brings him in contact with a member, Ariel Eberhart, fire-breeder at his favorite nightclub. She seems however romantically more interested in Nick than is safe for his relationship with Juliette, and is the daughter of the murdering 'dragon'.
Nick and Juliette join Hank for dinner, where Nick discovers Hank's mystery date is none other than Adalind, the same Hexenbiest who tried to kill Aunt Marie. Meanwhile, Captain Renard takes matters into his own hands when a visit from foreign representatives of his royal bloodline threatens his position. Elsewhere, Monroe and Rosalee are called into action when the lives of Hank and Sgt. Wu hang in the balance.
While investigating a string of murders, Nick and Hank learn that their suspect's crime wave began overseas. When Nick discovers the suspect is being harbored by none other than Monroe and Rosalee, he realizes he's hunting the hunted, a freedom fighter trying desperately to escape the clutches of a creature bounty hunter.
Nick investigates the murder of a bridge construction contractor who is a beaver (Eisbiber), by a building inspector who is a troll (Hasslich). The contractor's refusal to pay tribute to the inspector potentially disrupted long history of trolls controlling bridges.
After a man and his wife are scammed out their fortune by a Madoff-like fraudster, the husband approaches his wife's evil stepmother for financial assistance. But she refuses and is soon after murdered by a Murcielago - a bat-like creature that kills with a sonic scream.
Episodes of vicious attacks by Bigfoot-like Wesen known as Wildermann are suddenly rampant. Nick and Monroe discover that the errant Wesen are connected to a psychologist performing medical experiments to help the Wesen control their urges.
A Siegbarste Wesen wreaks havoc while searching for the ancient Zakynthos gold coins, while a mysterious woman in black tracks his movements. Nick informs a dubious Juliette of his heritage just before she collapses and is hospitalized because of a poisonous scratch from Adalind's cat.