A mysterious present is delivered to a Christmas party. After all the guests leave and the hosts go to sleep, a gremlin bursts out of the box. With a couple of its friends, it proceeds to wreck the house and beats up the homeowner who goes down to investigate the ruckus.
Monroe prepares for Christmas in his usual holiday splendor, including extravagant train set, and invites Rosalee to a long-delayed honeymoon.
Trubel, Hank, and Nick read up on the hate group that is targeting Monroe and Rosalee; it makes the Inquisition look like a day at the beach with burnings at the stake and other similar horrors directed at "impure" Wesen.
Juliette and Josh talk about Josh's father and what it means to be a Grimm. Josh laments the loss of his old life and wonders whether he will ever come into Grimm powers like Nick and Trubel.
Nick and Hank investigate the destruction at the Gladstone house. They realize that the attackers came out of the present that was delivered to the house and find fruitcake crumbs on the floor.
Trubel tries to sneak out of the house, past Josh who is sleeping on the couch, but he wakes up and insists on accompanying her in order to learn more about his Grimm heritage. She reluctantly agrees. They go to the home of Shaw the Klaustreich, the one who had threatened Nick. Trubel gets caught by one of Shaw's friends, a Schakal, but Josh hits him on the head and they make their escape. They realize that Shaw's and his buddies may be related to the Wesen hate group that is causing problems for Monroe and Rosalee.
Renard warns Nick that Elizabeth is searching for Kelly Burkhardt and the baby.
Nick and Hank get called to the scene of another gremlin attack and manage to capture one of the little menaces. They lock the creature in a cage at Monroe's house with Juliette and Rosalee and go to the trailer to learn more.
The discover that the gremlins are Kallikantzaroi, but they aren't actually their own type of Wesen. Rather, they are kids of another type of Wesen that are experiencing rapid hormonal shifts and messes that are making them that way. The only solution is to gorge them on fruitcake.
The Kallikantzarus that they captured escapes after its friends catch them, causing damage to Monroe's living room. As Monroe and Rosalee are cleaning up, they find a medic alert bracelet that belongs to one of the kids, giving them his identity.
Nick and Hank requisition a fruitcake truck from a local vendor and use it to set a trap for the Kallikantzaroi. The gremlins are lured into the truck, and they lock them inside until morning, whereupon they revert to normal.
Trubel tells Nick that she's going to Philadelphia with Josh. He gives them his aunt's old car to get them there.
Juliette looks worriedly at a home pregnancy test.