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 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.

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.

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.

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.

Nick's destiny is uncertain as zombies continue to overrun Portland.

A series of disturbing crime scenes leads Nick (David Giuntoli) and Hank (Russell Hornsby) to the resurrection of an old feud that's all too familiar for Nick and Monroe (Silas Weir Mitchell). 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 (Bree Turner) talk about moving their relationship forward.

When Nick (David Giuntoli) and Hank (Russell Hornsby) investigate a drowning death with mysterious marks on the victim's ankles, they happen upon a group of water-bound Wesen. Meanwhile, Rosalee (Bree Turner) starts unpacking her things at Monroe's (Silas Weir Mitchell), and Captain Renard (Sasha Roiz) makes a startling realization about the possible identities of the Royal Baby's parents.

When investigating a series of brutal murders committed on criminals, to Nick it appears that the culprit may be a character from a Latino legend.

An old urban legend from within Portland sewers comes to light when a murder is committed by an vicious, alligator-like wesen.

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 Juliette to surprise Rosalee for their first Christmas together with unintended results. Elsewhere, Captain Renards tour of Europe brings him closer to tracking down Adalind.

Nick (David Giuntoli) and Hank (Russell Hornsby) investigate a cop killer who scalps his victims. Meanwhile, Juliette (Bitsie Tulloch) begins to communicate with Nick's mom via email and Adalind (Claire Coffee) finds herself much closer to delivering her baby than she previously thought. Elsewhere, Monroe's (Silas Weir Mitchell) parents (guest stars Dee Wallace and Chris Mulkey) decide to surprise him and Rosalee (Bree Turner) with an early arrival to Portland after learning some exciting news.

Monroe (Silas Weir Mitchell) fights an impossible battle to convince his parents (guest stars Dee Wallace and Chris Mulkey) to embrace the life choices he's made. Meanwhile, Nick (David Giuntoli) turns to Juliette (Bitsie Tulloch) to help him figure out the Wesen aspect of his cop-killing scalper investigation. On the Royal Baby front, Captain Renard (Sasha Roiz) learns new information that forces him to contact Adalind (Claire Coffee) in the interest of keeping her and the baby safe from Viktor (guest star Alexis Denisof).

Nick, Hank and Juliette learn what the Wesen Community already know, the Wesen were GODS in ancient Egypt Meanwhile, Adalind and Meisner again run for their lives after a tortured Sebastien reveals the location where he dropped them off. Sgt. Wu, still fighting for his sanity is visited by Juliette. She tells Wu of her ordeal, which seems to have helped him because Wu is later picked up and taken home by Nick and Hank.

A double homicide leads Nick (David Giuntoli) and Hank (Russell Hornsby) 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 (Silas Weir Mitchell) and Rosalee (Bree Turner) 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 (Claire Coffee).