During the investigation of an accident site, Nick discovers a disease that is quickly spreading; Monroe and Rosalee come across an infected creature; Captain Renard gets a tip about a dangerous fugitive.

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.

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.

A panicked Juliette, Monroe, and Rosalee enlist Hank's help in fending off a zombie hoard while trying to figure out what happened to Nick. Knowing the truth, Captain Renard takes measures to help rescue Nick from the clutches of his brother, Eric. Elsewhere, along with the help of the mysterious Stefania, Adalind finds herself facing her most gruesome task yet in her effort to regain her Hexenbiest abilities.

A series of disturbing crime scenes leads Nick and Hank to the resurrection of an old feud that's all too familiar for Nick and Monroe. With the news of a royal family member's demise, several key players start to make their move. Meanwhile despite his recent trauma, Nick finds himself healthier than normal and Monroe and Rosalee talk about moving their relationship forward.

When Nick and Hank investigate a drowning death with mysterious marks on the victim’s ankles, they happen upon a group of water-bound Wesen with a deadly postcoital cuddle. Meanwhile, Rosalee starts unpacking her things at Monroe’s, and Captain Renard makes a startling realization about the possible identities of the Royal Baby’s parents.

Nick and Hank are on the case as repeat instances of apparent vigilantism have whispers of an old Spanish legend making their way through a working-class Portland neighborhood. Elsewhere, Juliette learns the truth about Nick’s mother. Meanwhile, Adalind has a brief scare during her ultrasound.

As a deadly crime spree begins to surface, a century-old urban legend takes shape in Portland's sewers and becomes Nick's latest case. In Europe, Adalind meets Prince Viktor, who’s come to bring those responsible for his cousin Eric’s demise to justice. Meanwhile, Captain Renard responds to the recent attempt on his life.

After a string of delinquent teens go missing, an old Wesen tale of an evil Santa who brings more than just a lump of coal may be the prime suspect. The investigation intensifies as Nick and Hank take things a little too far. Meanwhile, Monroe enlists Juliet to surprise Rosalee for their first Christmas together with unintended results. Elsewhere, Captain Renard’s tour of Europe brings him closer to tracking down Adalind.

Nick and Hank investigate a cop killer who scalps his victims. Meanwhile, Juliette begins to communicate with Nick's mom via email and Adalind finds herself much closer to delivering her baby than she previously thought. Elsewhere, Monroe's parents decide to surprise him and Rosalee with an early arrival to Portland after learning some exciting news.

Monroe fights an impossible battle to convince his parents to embrace the life choices he’s made. Meanwhile, Nick turns to Juliette to help him figure out the Wesen aspect of his cop-killing scalper investigation. On the Royal Baby front, Captain Renard learns new information that forces him to contact Adalind in the interest of keeping her and the baby safe from Viktor.

Nick and Hank find themselves thrown into the middle of an ancient battle and things heat up when the Wesen Council decides to get involved. Monroe and Rosalee fill everyone in on early Wesen history. Meanwhile, Sgt. Wu is still reeling from the events he recently experienced. As things heat up in Europe, one of the Resistance’s most trusted allies gets compromised as he tries to protect Adalind.

A double homicide leads Nick and Hank to a traveling carnival where the performers are not what they seem. To get a better understanding of what's going on behind the scenes Monroe and Rosalee go undercover. On the wedding front, Monroe has a really important question for Nick. In Austria, an invaluable member of the Resistance makes the ultimate sacrifice to help Adalind.