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.
As Hank continues to seek help to cope with the inexplicable siting he had, an old friend, Jarold Kempfer, needs his help when his daughter goes missing. Nick's expertise as a Grimm comes in to play as he investigates the disturbing motives linked to the disappearance.
While investigating an accident site, Nick comes upon a bizarre and gruesome Wesen disease that is spreading quickly. A romantic day out for Monroe and Rosalee takes a dangerous turn when they encounter an infected creature that is out for blood. Meanwhile, Captain Renard gets a tip about a dangerous foreign fugitive who's made his way to Portland.
When a local Reverend reports that his church has been robbed, Nick quickly learns that it's a Wesen church, and enlists Monroe to check for any suspicious activity regarding the shepherd's flock. Meanwhile, Nick and Juliette continue to figure out the rules of their relationship as a dangerous opponent lurks in the shadows with his sites on Nick.
Angelina comes back in to town with bad tidings as Monroe learns his continued cooperation with the Grimm may come at a high cost. Nick comes to Hank for help to keep Monroe safe and Hank uses this time to get caught up with his knowledge of the "Wesen world." Meanwhile, an old European acquaintance pays Captain Renard a visit, but it's hard to tell if this visit is for business or pleasure.
After investigating a grisly murder, clues lead Nick and Hank to a seemingly unstable father who is on the run with his daughter. As they learn more about the case they realize that the girl's father may be the least of their worries. At the spice shop, Monroe finds out filling in for Rosalee isn't as simple as he'd hoped it would be. Meanwhile, Captain Renard finds himself paying unwarranted attention to more than one woman from his past.
Nick and Hank are called to the scene of a murdered high school academic decathlete and learn just how competitive some extracurricular activities can be, and the extremes some coaches and parents will go to give students the best chance for success. In other police matters, Captain Renard deals with an unwanted infatuation while we learn an old accomplice of his has been spending time with his family in Europe. Elsewhere, Monroe continues to manage the spice shop and gets a visit from an unlikely customer.
Despite the enthusiastic anticipation of the city's residents for Halloween, a series of horrifying child abductions make their way to Portland, quickly spoiling the holiday spirit. Nick and Hank join forces with Valentina Espinosa, a mysterious detective from Albuquerque, to help find and capture the elusive suspect. Juliette joins their investigation, acting as the precinct's fill-in Spanish translator. The more Nick digs into the case, the more he realizes the pattern of the kidnapping matches those in the famed Hispanic horror story "La Llorona," a story with its roots intertwined with his own family's history. Meanwhile, Monroe celebrates the holiday in fine style as he teaches the neighborhood bullies a lesson.
When a brutal vigilante homicide is made public, it sends Portland's Wesen community into a frenzy. As Nick investigates further, he discovers a pattern similar to that of a particularly brutal line of past Grimms. Is there another Grimm in town, or is Nick dealing with a sadistic copycat? Meanwhile, Captain Renard takes it upon himself to offer Juliette comfort in handling her ongoing dilemma with Nick.
Hank starts reflecting on an arrest he made earlier in his career regarding a man who committed murder claiming "self-defense against monsters." With the man's death sentence rapidly approaching and the knowledge he's recently gathered from Nick, Hank begins to wonder if there was more truth to the man's seemingly absurd story then he once thought. Back at the spice shop, Monroe finds himself involved in a situation he never saw coming.
Adalind returns to wreak havoc in everyone's lives and avenge her mother's brutal death. She has her eyes set on Nick and those closest to him - especially Hank and Juliette. Elsewhere, Captain Renard's obsession continues to escalate. Meanwhile, a surprise visit at the spice shop gives Monroe more than he ever bargained for.
After Nick learns about Juliette and Captain Renard, he must deal with the consequences. Things get even more complicated when Nick is called to investigate his own crime. Meanwhile, the search for the key intensifies as Captain Renard finds Nick's trailer and makes a surprising alliance. With Rosalee's help, Monroe informs Nick that they might be able to stop what's going on with Renard and Juliette before it goes too far. Elsewhere, Wu responds to a bizarre shooting at Nick and Juliette's house.
The Wesen code of honor comes into question when Nick, Hank and Monroe discover a series of bank robberies with Wesen using true natures as their disguises. Meanwhile, Juliette finds herself tormented by faint, slowly returning memories that cause her to question her mental state.
When a mysterious case of sudden blindness causes a woman's death, Nick and Hank come across a disturbing Wesen that feeds off its victim's tears. Meanwhile, Adalind contemplates the significance of her new situation, while Juliette continues to work with Rosalee in an effort to fix her memory.
When a gruesome homicide brings an office party to a screeching halt, Nick and Hank find themselves battling a Wesen on a completely new platform - online. Meanwhile, Juliette's mysterious hallucinations finally start to take shape, giving them a whole new meaning.
While on jury duty, Rosalee tasks Nick, Hank and Monroe to help stop a defense attorney from using his particular "Wesen wiles" to overturn what should be an open-and-shut murder case. Back at the precinct, Captain Renard brings Nick and Hank in on his own recent dealings with the Verrat, to keep them on their toes. Meanwhile, a return to the trailer brings a flurry of memories of Nick rushing back to Juliette.
Nick finds himself fighting a wildly different sort of nature freak in a desperate attempt to keep a volcano from burying Portland in lava. Meanwhile a pregnant Adalind meets a powerful new ally in Europe. Meanwhile, Juliette seeks out help after becoming overwhelmed by the latest side effect of her recovery - multiple memories of Nick showing up everywhere.
Mysterious cow mutilations and reports of glowing creatures put Nick on a case that forces him to question the existence of aliens within the Wesen world. He also meets a strange UFO expert who seems to know more than he's letting on. Meanwhile, Nick digs further into the key, and Juliette's romantic memories of Nick start coming back in a big way.
Nick discovers a muse-like Wesen with the ability to influence those she gets close to - some with positive results, others with terrifying ones. Nick must find a way to get close without losing himself in the process. Juliette arranges a dinner date with Nick in the hopes of clearing the air, but their plans go awry as the case intensifies. Meanwhile, Rosalee takes her first visit to Aunt Marie's trailer.
Nick and Hank discover a new kind of strange when they investigate suspects being found dead - for the second time. In Europe, Adalind finds herself in the middle of a feud between Frau Pech and Stefania while working over the details of her pending transaction. Meanwhile, determined to remember every last detail to get things started once more, Juliette insists Monroe share with her Nick's darkest secret - the world of Grimms and Wesen.
Just when things look like they're back to normal with Juliette, Nick is called to investigate a flurry of rage-fueled assaults happening all over Portland. He goes to Monroe and Rosalee for help battling Portland's newest wave of "undead." As if that weren't enough, Captain Renard informs Nick that his brother Eric is in town on family business. Meanwhile, Stefania and Frau Pech methodically use their alliances with Adalind to battle one another.