After their face-off with Kimura, Nick finds himself trying to come to grips with the return of his mother, Kelly Burkhardt. A trail of brutal murders unveils a foreign conspiracy to hunt down Nick, leading to several revelations about his past. Meanwhile, Juliette still lies in her mysteriously-induced coma as Rosalee and Monroe work tirelessly to bring her out of it safely. Elsewhere, Hank struggles with the shocking truths he's recently seen and Captain Renard deals with unexpected family issues when his estranged brother comes back into his life.

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 Walkers, 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 over for a home cooked 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 Monroe's death to warn him after 'accidentally' killing the initial hit man. Nick, who wants her for at least two earlier murders, grudgingly cooperates, going so far as to allow her to pretend to be his partner. To get to the royal presumed to have hired the killer, Monroe must fake his death with a potentially lethal potion, instructed over the phone by Rosalee, who visits a very ill relative, after a dream date with Monroe. The royal is in awkward league with Renard.

An unsettling murder scene leads Nick and Hank to what looks like a bitter custody battle.

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 cross breed. In Vienna, Renard's brother, Prince Eric, confides unto his latest conquest.

On Halloween, Nick and Hank search for a figure from Mexican folklore who might be abducting children; meanwhile, Monroe tries to deal with some troublesome trick 'r treaters.

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 Nick messages, suggesting he is a 'real Grimm' who is cleaning up 'weakling' Nick's messes. But he strikes terror even with gentle Wesen, like the beavers, who seek help through Monroe, who fears it's a descendant of a medieval Grimm vigilante order. Nick suspects a police mole.

Hank's knowledge of Nick's world has him second guessing a past case.

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 Juliette's partner, who ordered an obsession cure, is none other than Police Captain Sean Renard and ends up telling Nick. Meanwhile Adalind and a pack of canine Wesen almost hunt down Renard for the key, and he locates 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. Assisted by just returned Rosalee, 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 ever, 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 enforced. Juliette has novel supernatural experiences at home.

Those grieving for a deceased loved one becomes the target of a revolting fly-like Wesen who feeds on tears and leaves behind a deadly parasite.

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.

A young geologist is gruesomely burned after collecting rock samples from a nearby volcano, and it finds Nick and the rest trying to stop a demonic Beast who is literally hot to the touch.

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 seven crusader Grimms. Juliette swears Monroe to secrecy, being insecure about her reemerging love memories.

When Nick encounters a muse-like Wesen after the murder of her boyfriend by her jealous ex-lover, things start to get a little complicated.

A mysterious drug related force begins to turn residents of Portland into feral zombies, meanwhile, Juliette learns more of the wesen community in the spice shop.

Nick is back on lovers' terms with Juliette, who remains eager to learn about ferals. Nick must however give priority to the violent crime 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 Eric had prepared at the castle. Still in Vienna, Adalind, poisoned by Pech to switch appearances, is seen roughly overtaken by the gypsy witch's family Popescu. Rosalee prepares a zombie antidote, but once tracked down in the port, the superior zombie numbers corner down Nick's party.