Facing their far and family feral past shakes up the Seattle PD protagonists. Nick joins forces with his death-presumed mother Kelly Burkhardt, a huntress who followed Akira Kimura, to chase the excessively cruel 'mauvais dent' monster murderers, who are after six golden coins, part of the key to a terrible secret since the crusades. It's the obsession of rivaling feral royalty branches, including Renard's, putting him opposite his estranged European half-brother.
As Nick and his mother continue to battle the Mauvais Dentes, Monroe and Rosalee fight against the clock to save Juliette. More details are revealed about the source of Juliette's illness, resulting in an epic showdown. Back at the precinct, Hank senses that something is amiss when Nick lands in hot water with the FBI. Meanwhile, Captain Renard continues to reveal himself as he deals with his estranged brother.
Monroe explains to Nick about the feral Coyotl prison gang-like, even tattooed kind's pack code when they find on old friend of Hank is actually one who fled his pack years ago and now finds his daughter kidnapped. The trail leads to their Texas relatives, the Kempfers, who stop at nothing but ignore the other side has a Grimm. Nick shows angelic patience when Juliette's memory returns about everything except their love.
Park ranger Ryan Gilko is the first of several Wesen, affected by a contagious disease, who suddenly commit violent attacks on people. The team felt relaxed now Hank is being included in the secret, so Monroe takes Rosalee on a picnic. Alas, the plague spreads and even affects her, so it's up to Monroe to make the remedy they researched together while Nick holds her feral state in check. Captain Renard meanwhile learns that another terrifying European fugitive has arrived in Portland.
Reverend Calvin, a feral wolf, reports a fortune stolen from church funds and the parishioner who did the accounts, a feral sheep like most of his flock, missing. The man is later found cut-up in the grinder of his employer's factory, but has no motive or suspicious record. Undercover as a 'homeless' seeking church shelter, Monroe discovers reverend Calvin, whose previous Southern parish was similarly robbed presumably by a parishioner, has an affair with his sheep church secretary, who transferred with him, but is up for a rude surprise too.
Nick is delighted when Juliette, who still can't remember him, invites home for a home dinner to get acquainted all over. But he's called away urgently by Monroe, who has a feral visitor: a ruthless killer, yet also a friend of his, who only pretended to take a contract for his death to warn him after 'accidentally' killing the initial hit man. Nick, who wants her for at least two earlier murders, grudgingly cooperates, even has to allow her pretending to be his partner. To get to the royal presumed to have hired a killer, Monroe must fake his death with a potentially...
Even Nick is puzzled by the case of two murdered teenage favorite candidates to the high-school general knowledge quiz qualifying for the state competition. Wesen in the story belong to several species, one extremely rare. Captain Sean Renard wins a community prize and turns to Monroe for a medicinal cure for his sexual obsession with Juliette Silverton. Surviving competitor Pierce Higgins is actually an unwitting Wesen-halfbreed. In Vienna, his brother, prince Eric, confide into his latest conquest.
When Mexican immigrant Alvarez tries to save a woman in white from drowning herself in the river, the actual ghost abducts his small son Rafael. The next day, a girl suffers the same fate. Valentina Espinosa, an Albuquerque detective, arrives to offer the Portland PD here expertise in many similar trios of abductions ending in the children's midnight drowning by a strict MO. It ties in with the legend of La Llorona, but the FBI reports her fired and illegally intruding the investigation. Nick finds that the ghost in a Wesen.
Nick is puzzled by several cases where a suspect who escaped the police is violently dealt with by a masked, cloaked avenger. He even leaves messages, suggesting to be a 'real Grimm' who cleans up 'weakling' Nick's messes. But he strike terror even with gentle Wesen, like the beavers, who seek help trough Monroe, who fears it's a descendant of a medieval Grimm vigilante order. Nick suspects a police mole.
Nick is shocked about Juliette's infidelity, which she can't explain, yet sort of accepts it and ends up moving out to his heritage trailer. Monroe realizes from a TV appearance that her partner, who ordered an obsession cure, is none other then police captain Sean Renard and ends up telling Nick. Meanwhile Adalind and a pack of canine Wesen almost hunt down Renard for the coin, and he tracks Nick's trailer after allowing him to lock up Adalind.
Once Monroe shows him that Renard is Juliette's lover, Nick can barely control the urge for illegal revenge. Helped by just returned Rosalind, Monroe works out how the passion spell can be broken, and ultimately Renard convinces Nick they must work together. Meanwhile Adalind is released for lack of evidence and returns to Renard's traitor brother in Vienna, without the key, not knowing Renard found and stole it from Nick's desk.
Monroe's potion finally relieves Renard and Juliette's passionate obsession, so he and Nick can collaborate again, even closer then even, with Monroe and Hank aboard, against the royal conspirators. Three youngster Wesen, Cole Pritchard, his girl Krystal Fletcher and his former cell-mate Gus, repeatedly commit robberies using their Wesen appearances as if masks. Monroe witnessed a bank robbery and alerts Nick's police team as well as the 'Wesen Council', as this is a blatant violation of the centuries old Schwaben code, which Amsterdam HQ chief De Groot orders ...
Shortly after each-other, people are attacked by a revolting fly Wesen, which causes blindness by licking, thus introducing river blindness-type parasitic worms. Nick is affected himself. Monroe and Rosalind work out they only have a few hours to prevent permanent blinding by capturing the Wesen in feral form, scooping up an eye and mixing it in a concoction. So they must find it even faster, using heirloom Grimm record clues.
In Dominick Spinner's successful Portland games design company, several employees engaged in developing and testing a single video-game are, one by one, killed i the game and hours later for real, by similar gruesome devices. At each corpse a literary clue is found, an anonymous caller dares the police to identify him. Nick handles the case, using Wu's bachelor hobbies experience. Monroe helps work out what rare Wesen could be behind it. Renard is preoccupied with royalty parties rivalry.
After sleeping on it Nick decides it would be best for Monroe to take Juliette to the trailer. However, the trailer triggers more memories of Nick than Juliette may be able to handle leading her to seek the help of Pilar for insights into her current condition. Meanwhile Monroe fears Rosalee, who is serving jury duty, maybe under the influence of a toad dropping Ziegevolk who is jury tampering to win his case. Nick, Hank, Bud, Monroe and Rosalee hatch a plan to stop this Ziefevolk once and for all.
While Hank goes on vacation, Nick and Renard team up to investigate the death of a local geologist who was cooked from the inside out after taking volcanic rock samples from Mount Hood. Meanwhile in Austria, Frau Pech takes Adalind to a Gypsy woman to learn the value of her baby, but the former Hexenbiest desires something other than money.
Ranchhand John is killed while accidentally bumping at night into Vincent, a blue-fluorescent feral performing one of the 27 raids on cows that went from Nebraska to Portland, actually harvesting bovine ovaries for his pregnant mate Jocelyn, with whom he keeps moving and hiding. Besides Nick, the case seems to be followed only by an 'ufologist' or alien-hunter, who in fact chases the very feral species. Monroe recognizes the print Nick made from his key as part of a medieval map as Swabia, Renard explains the keys combine into a map to a terrible treasure hidden by ...
A Caribbean feral, called 'bouckman' in the Grim records, causes his victims to get green foam around the mouth. Only apparently dead, they arise as extremely violent zombies. Their feral created in Portland, a voodoo 'baron', is in league with captain Renard's rogue brother Eric, who visits from Vienna to discuss dynastic matters. It concerns a royal bastard child, equally dangerous and valuable, born by Hexenbiest Adalind, who is torn between conflicting advise and tricked into 'signing' a gypsy-style contract. Meanwhile Monroe, Rosalee and beaver Bud oblige ...
Nick is back on lovers terms with Juliette, who remains eager to learn about ferals. Nick must however give priority to the violent crimes wave caused by zombies. As he feared, they are created by the voodoo 'baron', who sets a trap as instructed. Captain Sean Renard informs Nick about his mistrusting meeting with visiting European royal half-brother Eric and the counterfeit documents he prepared at the castle. Still in Vienna, Adalind poisons with Pech to switch appearances, but is still seen trough and overtaken by the gypsy witch's family Popescu. Rosalid prepares ...