Plot
Jordan Sands (Victoria Justice) is an awkward and nerdy 17-year-old girl with a bad case of allergies who became the woman of the house after the recent death of her mother. Her father, David (Matt Winston), struggles to make ends meet, while her 14-year-old brother Hunter (Chase Ellison) drives the family crazy with gory pranks as he loves monsters. They inherit their mother's great uncle Dragomir Vukovic's castle in Wolfsberg, Romania, which they did not know existed. After arriving in Wolfsberg, they meet the strange and steely castle housekeeper, Madame Varcolac (Brooke Shields), whose name, when pronounced, causes a wolf to howl in the distance.
Meanwhile, the kids explore the town. Hunter learns about the "Wolfsberg Beast," a monster that protects both the castle and the town, and Jordan falls in love with the local butcher, Goran. Varcolac discourages David from selling the property, but he decides to do so that they can end their financial struggles. He dates with the bubbly real estate agent Paulina von Eckberg, who handles the selling and only appears at night.
One day, while snooping around Dragomir's lab, Jordan accidentally steps on a vial of blood. Though Hunter pulls the bloody glass from her foot, her behavior changes. She becomes a carnivore (at the beginning of the movie, she mentions having tofu stir-fry for dinner because of her vegetarian diet), her senses heighten, gains a playful dog-like behavior (she plays with the dogs at a nearby park), and her allergies disappear. Hunter's friends explain that Jordan has become a werewolf due to either a bloodline curse, a werewolf bite, or becoming infected with the blood of a werewolf. Hunter realizes it was the vial of blood, which is revealed to have been LB-217, short for "Lycanthrope Blood."
Jordan transforms into a werewolf, which Hunter witnesses. She holds back from attacking Hunter and flees. Hunter's friends reveal that there is no cure they know of other than killing a werewolf with a silver bullet. Hunter refuses to do this. His friends warn that if Jordan is not cured by next sunrise, she will remain a werewolf, cursed to shift every night until the end of her life.
Hunter turns to Varcolac, who reveals that Dragomir was also a werewolf and was the famed "Wolfsberg Beast." Vampires attempted to take over the castle and rise to power, but Dragomir stopped them before he was killed. Before his death, he had been working on a cure for lycanthropy. As Varcolac quickly gathers the ingredients for the treatment, Paulina captures the siblings, revealing herself as a Vampire and the one who killed Dragomir. She wants to take over the manor, but must kill Jordan first, as she is unable to take the castle as long as Dragomir's werewolf relatives are alive. Jordan is restrained in her werewolf form while Hunter escapes and leads David to the hideout. However, they are also captured.
Before Paulina can shoot Jordan, Hunter suddenly turns into a werewolf, as he is part of the bloodline, making him a true descendant, unlike Jordan. The siblings fight the Vampires until the sun rises, and the Vampires are killed in the sunlight. In the manor, Hunter's blood is used in the antidote, and it successfully subdues Jordan's werewolf self and reverts her to normal. The Sands family formally receives the money they inherited from Dragomir, which is enough for them to keep the castle and their original home, as Dragomir had supposedly invented karaoke. Hunter becomes the Wolfsberg Beast, his true destiny, and takes Dragomir's place.
The family returns home, where Jordan demonstrates a new confidence at school. Goran also moves to California as a foreign exchange student, and they start a relationship. In a twist, Paulina somehow survived and moved to their neighborhood to continue her attempts at taking over the castle.
The movie ends as the cast sings and dances to "...Baby One More Time" on karaoke.
