Nick Burkhardt, a promising Portland homicide detective, told nobody he's been seeing 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, narrowly escaping. Nick discreetly uses his gift to track down a postman, who turns out to be a descendant of werewolf lineage, and who helps him find the violent monster.

A case of breaking and entering introduces Nick and Hank to a mysterious family whose cultural background blurs the line of right and wrong. Meanwhile, Nick tasks Monroe with safeguarding Aunt Marie.

During a flash-mob on a bus, a lawyer is killed with a stunning overdose of bee venom, but it fits no geographical origin. Monroe and the Grim records help Nick work out it must be the work of a feral bee queen, the sworn enemy of Hexenbiests like Adalind. Trailing a professor-beekeeper and the other twelve attendants of a bee-keeping convention, Nick and his partner Hank find them congregating and get attacked by an unnatural bee swarm.

Nick learns that a series of disappearances, rapes-and possibly murders-of beautiful women in the Portland area is connected to a honeymoon hotel where the owner harbors a hypnotic power.

Nick investigates the death of a music teacher who was eaten alive by rats whille locked in his own car. Nick and Hank are led to a expelled music prodigy who has a strange sort for vengeance against those who wronged him.

Blutbad Hap Lasser coincidentally survives a cunning arson attack which makes his home explode, two months after his brother died in a similar fire. Monroe reluctantly takes him in, also as a favor to Hap's sister, Monroe's own ex-lover Angelina. She returns to revenge both brothers and hates Grimms but resumes nocturnal hunt fun with Monroe. Lieutenant Peter Orson didn't call either case arson, but lost his own brother in a fire which may be a Blutbad's doing.

When a hiking couple is saved from a drug trafficker from what appears to be a "Feral Beast" nick investigation into it leads to the suspicious that it is linked with a 10-year old missing persons case.

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.

A man named Leonard "Lenny" Drake is found dead in a garbage truck and Nick and Hank investigate the case. They find blood in the dumpster near his building and a trail of blood to the parking garage. The manager explains that the tenant was a violent man that lived in his apartment with the gorgeous Natalie Havershaw. On the previous night, they had an argument and the tenants Marty Burgess first and the lawyer Mason Snyder then had come to protect her. Marty returned to his apartment while Lenny and Mason continued to argue. Then Mason escorted her to her car and she left the building to check in a hotel. Nick and Hank visit Marty at his junk shop and Nick sees that Marty looked like a mouse. Then they visit Mason and Nick sees that the lawyer looked like a snake. Nick visits Monroe and learns that the creatures are the harmless and cowardly Mauzhertz and the dangerous and lethal Lausenschlange respectively. Then Monroe receives a phone call relative to work and Nick leaves him, but Monroe receives a message instead. When another man is found dead in the dumpster of a repair shop in the same "modus-operandis" Nick believes the cases are connected.

While investigating the death of a homeless teen, Nick and Hank uncover a ring of Geiers harvesting human organs. Also, the Verrat threaten Captain Renard to keep the Grimm under control.

Nick and the police department goes on the hunt for a mysterious wesen woman who first seduces men and then gruesomely murders them in a "Arachnid"-related death.

When Nick consults him about an erratic murder committed by athletic ex-con Dimitri Skontos, Monroe 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 through 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 the games is ignored, so he turns to a priestly enforcer. Meanwhile first Monroe, then Nick go undercover, only to end up caged and hence in the ring, facing daunting ferals.

Jeweler Sam Bertram was murdered by three European 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 absolute power in Nazi style.

When heavily burned bodies appear, Nick learns of the existence of dragons in the world of wesen and a charismatic fire-dancer tries to spark a flame between herself and Nick, hiding a deadly true agenda.

Nick investigates the robbery of a spice shop, that is owned by wesen, discovering that the thieves were after a dangerous drug.

Nick and Juliette go away for a little R & R. They meet a couple who turns out to be not human. Juliette meets the wife and senses she's being abused. Nick learns the man is a being who abuses women.

Nick is in the trailer trying to find out what the key that he received from his aunt might open. Juliette calls him telling that Hank has invited them to have dinner together with Adalind. Captain Renard is forced by a criminal with a weapon to go with him to meet his cousin, but he reacts and kills them both. When Nick meets Adalind, he recalls that she wanted to kill his aunt and he confronts her near the restrooms. But he is called to investigate the murder of the two men and leaves the restaurant. Meanwhile Renard goes to the house of Catherine and she tells him that her daughter will get the Grimm's key for him. Nick meets with Monroe and Rosalee and Rosalee discovers what Adalind gave to Hank. Will she be capable to prepare an antidote and save his life?

A man named Ian Hamon is being hunted down by the Verrat's agent Edgar Waltz and is wounded at Portland's bus station by a bullet and loses his backpack. Waltz meets Captain Renard seeking for help to capture Ian but his request is turned down. Meanwhile, Ian, who belongs to the Wesen Resistance, goes to the spice shop and Rosalee, who was his lover in the past, calls Monroe to help her to remove the bullet. Waltz kills a man and leaves Ian's passport in the crime scene to force Renard to chase him. When Nick arrives at the spice shop, he tries to arrest Ian, but Rosalee and Monroe testify that he was unconscious with them when the man was murdered. Soon Waltz confronts Nick while Ian needs a new passport to leave the country. Nick has to make a decision and cross the line as a police detective.

Nick searches for the potential witness to the murder of a bridge construction contractor caused by a troll-like wesen.

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 Schakal 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.