Nick and Juliette struggle with the loss of his powers, while Monroe and Rosalee postpone their honeymoon to help out. Nick, Hank, and Trubel investigate a Gedächtnis-Esser (octopus-like wesen), as Capt. Renard lies in critical condition. Meanwhile, the Grimm Diaries that Trubel owns in the guest room of Nick's house attract unwanted attention from Wu and Special Agent Chavez.

Capt. Renard dies while in the hospital, but only for a moment as his mother, Elizabeth, revives him with her powers and abilities. Meanwhile in Austria, Viktor locks Adalind in a Hexenbiest-proof dungeon. Nick and Hank send Trubel by herself to keep an eye on the Gedächtnis Esser.

Nick and Hank investigate a Wesen boxing gym while Elizabeth helps Monroe and Rosalee search for a way to restore Nick's powers. Trubel keeps her eyes on a young wesen boxer in his teens named Clay who is a Heftigauroch (bull-like wesen), and his wesen boxing trainer named Stan who is a Schinderdiv (warthog-like wesen).

Nick and Hank investigate a possible homicide where the victim was Keith Harrow, Sara Fisher's abusive ex-husband & a wesen called siegbarste (ogre-like wesen). It appears that he has died from asphyxiation by clay. It turns out he was killed by a Golem who was called upon by the Rabbi brother of the victim's ex-wife, Ben Fisher. Trubel's presence still doesn't sit well with Wu. Elizabeth finds a way to restore Nick's Grimm powers, but requires a special something to make it happen.

Nick and Hank investigate a vehicular manslaughter case where the driver turns out to be a rich heir being driven to madness by her Luison (Wolf-like wesen) quadruplet husband named Gabriel and his three brothers. Bud enlists Trubel to deal with a possible threat to Nick's life. Nick and Juliette deeply consider whether or not to regain his Grimm abilities, since the process comes with a significant catch. When Monroe and Rosalee are threatened by the Wolfsangel, Juliette tells Nick that he must become a Grimm again.

Juliette tells Nick that he needs to be a Grimm again after the most recent attack on Monroe and Rosalee regarding their marriage. Later, Nick and Hank investigate a weird and unusual sacrificing wesen ritual by a Phansigar (Komodo dragon-like wesen). Nick finally gets his Grimm power abilities back. Trubel deals with being watched by another agent who works for Chavez, as well as Josh Porter arriving on the scene.

Monroe has a unique Christmas surprise for Rosalee. Trubel and Josh work together to track down the Wesenrein with gleichheit (equality) masks who keep threatening against Monroe and Rosalee's mischehen (mixed marriage). Meanwhile, Nick and Hank investigate a series of strange home invasions and uncover a bizarre Wesen phenomenon called kallikantzaroi (malevolent goblins-like wesen), with a rare genetic disease disorder during adolescence that wreaks havoc on Christmas unless they eat fruitcake until sunrise. Then the children of Indole Gentile (deer-like wesen) are back to normal.

An unsuspecting traveler brings a blood-sucking cryptid – the legendary "El Chupacabra" – to Portland, and Nick and Hank investigate. Wu confronts Nick about what he has seen about the Grimm Books and Nick's odd behavior. Monroe and Rosalee prepare to embark on their honeymoon, but are threatened once again by the Wesenrein.

Opening quote: "Cuide su rebaño, nunca deje su lado. Cuide su sangre, el Chupacabra tiene hambre."

Nick and Hank recruit Wu to help after revealing him to the world of Wesen. After Monroe gets kidnapped by the Wesenrein, the team must find out where he is before he is sacrificed and killed. Juliette's attempt to cope with transforming into a Hexenbiest is put on hold while she tries to tend to an anxious Rosalee.

Monroe is on trial by the Wesenrein for a ritual that is performed called the "Tribunal". Nick and Hank train Wu to deal with woged wesen, which allows him to confront Officer Jesse Acker, who is secretly a part of the Wesenrein, but without leverage, he cannot force him to turn on the group. Juliette and Rosalee scour the wedding guest list, provided by Trubel, with help from Bud, to find anyone who would have exposed them to the Wesenrein.

Monroe and Rosalee finally leave Portland to head and embark on their honeymoon, but this doesn't mean trouble somewhat isn't stirring in Portland. Nick, Hank, and Wu investigate a shocking homicide of a ghost hunter at a supposedly abandoned residence. Portland residents think it is haunted by a ghost; but Nick, Hank and Wu discover that an electric eel-like wesen called a Matanca Zumbido is responsible. Juliette's startling revelation to Captain Renard leads her to a longtime family friend from his past, a mystical woman named Henrietta (Garcelle Beauvais).

Nick and Hank investigate the murders of Wesen Fortune Tellers who have been using their woge in a scam to get money, which involves the Wesen Council and a manticore bounty hunter of theirs. Juliette meets up with Henrietta (Garcelle Beauvais) and is given bad news. Viktor and Adalind head back to Portland from Austria to find baby Diana's whereabouts.

During an investigation of an arson case that involves an Excandesco (phoenix-like wesen), Nick is forced to turn to a Bauerschwein arson investigator Lt. Peter Orson (Daniel Roebuck) whom he had put behind bars. Viktor teaches Adalind about well-played diplomacy and she attacks Juliette. Nick learns Juliette is a hexenbiest.

After Nick finds out Juliette has become a Hexenbiest he visits Henrietta, who says there is no cure and Nick must kill Juliette or accept her new status. He cannot cope with the change though, leading Juliette to leave. Meanwhile, Nick, Hank, and Wu investigate the murder of a teenager whose foot was cut off. They discover the victim was a Willahara (rabbit like wesen), whose foot was cut off so a couple could improve their fertility. Monroe and Rosalee go undercover to a Wesen fertility clinic to find the killer. Adalind meets Renard, who says he knew of Juliette's change and sent her to Henrietta to learn more. Adalind pays Henrietta a visit to understand the extent of Juliette's powers but instead learns she is pregnant with Nick's child.

Nick and Hank investigate a crime scene in the middle of a bizarre love triangle involved a flatworm like wesen called huntha lami muuaji. Captain Renard seeks Monroe and Rosalee's help to stop phantom bleeding when he was shot by Weston Steward. Adalind asks for a favor that could change the course of Juliette's relationship with Nick. Juliette faces a tough decision about her future with Nick.

Nick and Hank investigate the homicide of a cyclist named Zack and they meet a foterseele (golden/poison dart frog like wesen) named Bella Turner with a tragic poisonous touch of The Tale of the Frog Prince. When the King from the Royal family shows up in Portland, Captain Renard and Adalind realize the Royal family have stepped up their efforts to find Diana. Juliette ponders whether to embrace her new self or get rid of it.

Nick, Hank, and Wu are called to investigate a rare Wesen that leaves its victims frozen solid, a hibernacula called Varme Tyv. Meanwhile, Juliette starts to feel she is losing her humanity as she seeks to get revenge against Adalind. Elsewhere, Captain Renard continues to suffer from mysterious bleeding and visions, while Monroe works toward coming to grips with the Wesenrein incident.

Nick and Hank newest investigation is on a homicide in the dark and mysterious path of a local Native American "vision quest" involved mishipeshu (underwater Panther). Juliette's errant behavior lands her in trouble with the wrong side of the law. Monroe and Rosalee are on mission with Captain Renard's assistance. Hank falls prey to a Native American's spirit with yellow eyes.

Nick and Hank investigate a homicide and they learn it's connected to an age-old rite of passage for Wesen boys. Meanwhile, Juliette meets a surprising ally. Captain Sean Renard battles the darkness within and Nick finds hope for Juliette in the last person he expected: Adalind. Juliette makes a last visit to Aunt Marie's trailer.

A string of homicides have the press asking Captain Renard if a Jack the Ripper copycat has arrived in Portland. During the investigation, Nick, Hank, Monroe and Wu deal with a situation they never expected. Meanwhile, Adalind and Rosalee must work together on a last ditch attempt to fix Juliette's condition. Elsewhere, Juliette decides to help her new ally even if it means hurting those around her.

Nick and Hank investigate a grisly murder get closer to uncover the identity of the vicious serial killer while Wu's life is in grave danger. Monroe & Rosalee try to help Captain Renard to heal him from his visions and bleeding. Juliette solidifies a new alliance as she works to get revenge which gets Nick's mother killed. Elsewhere, Trubel is back in Portland from Philadelphia to surprise them.

After the shocking discovery of his mother's death, Nick is determined to get revenge and take the fight to the royals with Trubel's help. Meanwhile, Juliette's alliance continues to lead her down the dark path.