Tony Thompson [Jonathon Lipnicki] is lonely and friendless. His parents, Bob and Dottie, have just moved him from San Diego, California to Scotland, and the two McAshton boys, Nigel [Iain De Caestecker] and Flint [Scott Fletcher], are making fun of him at his new school because of his obsession with vampires. Unfortunately, Nigel and Flint are the grandsons of Lord McAshton, Bob's boss.One night, a bat flies into Tony's room. The bat is Rudolph Sackville-Bagg [Rollo Weeks], vampire, and he's in a bad way. He can't fly, and the vampire hunter Rookery [Jim Carter] is looking for him. Rudolph desperately needs blood and asks Tony to lead him to a cow. While Tony waits for Rudolph to finish his dinner, Rookery attempts to run Tony over with his vampire-hunting mobile, but Rudolph saves him just in time. Tony and Rudolph are now tit-for-tat, each having saved the other. They decide to become friends. Rudolph sleeps the next day in Tony's toybox but is gone when Tony gets home from school. Rudolph shows up again that night, asking about a picture Tony drew of an amulet he saw in a dream, the amulet of Attamon, made by the Great Magician from a piece of the comet of Attamon. Tony offers to help Rudolph find it because it could mean the end of a curse that causes Rudolph and his family to remain vampires. Unfortunately, Rookery is also seeking the amulet because, used in another way, it can send all the vampires straight to hell. Suddenly, Rudolph's family shows up...father Frederick, mother Freda, sister Anna, and brother Gregory. Frederick is not happy that his son has befriended a human. Just then, Rookery shows up and starts firing stakes at the vampire family. Tony cuts the hose between Rookery's stakegun and his pneumatic air supply. The vampires and Tony take refuge in an underground crypt, and Tony has a vision in which he sees a woman covering the body of the Great Magician with a blanket bearing a crest flanked by two stags and a banner reading "Sola animo at manuforti."Later that night, Tony and Rudolph pay a visit to the McAshton boys. Tony presents himself as the Lord of the Underworld and Rudolph as "the fiendish friend of Tony Thompson," and orders the boys to treat Tony with respect or else they will be bat-bait. The next day at school, the McAshton boys trip all over themselves to be nice to Tony. It appears that Tony's problems with the McAshton boys are over. However, his problems with the McAshtons are just beginning. That afternoon at tea, Tony's dad shows him a picture of the McAshton crest. Lo and behold, it is the one from Tony's vision. Later that evening, Tony goes to the crypt to tell Rudolph of his discovery, only to find Rookery there. Rookery lowers a bright light into the crypt, but Tony throws a rock at it and breaks the bulb. Unfortunately, Rudolph's father takes the full brunt of the light and is severely weakened. After fortifying their dad on some cowblood, the vampire family moves into Tony's cellar in order to hide from Rookery. During the night, as Tony tries to sleep, Anna [Anna Popplewell] comes into his room. She gives him a good luck charm (a dead mouse) from the old country and tells him to whistle if he should ever need her help.It's Saturday morning, and Tony goes to work with his dad, hoping to learn more about the McAshton crest and the whereabouts of the amulet. Unfortunately, Rookery is also there, and Lord McAshton is telling him about the family history. It seems that the woman in Tony's vision, the one in which he sees her covering the body of the Great Magician with a blanket that bears the McAshton crest, was actually Lord McAshton's ancestor, Elizabeth, and the Great Magician was the vampire Von Sackville-Bagg. Even more important is the fact that Elizabeth is wearing the amulet of Attamon in a family portrait and was probably buried with it. Rookery asks where she is buried, so Lord McAshton takes him to the family crypt. They open her coffin, but it is empty. Most likely, she was buried elsewhere, but where?Tony, who has been watching from a balcony, suddenly falls off...right into the coffin. Rookery, who has also been after Tony, closes the lid. Tony can't get out, but he remembers his good luck mouse and whistles for Anna. Although it is daylight, Rudolph and Anna cover themselves with a blanket and helmets and go to Tony. A mouse leads the three of them to a secret passage in which they find the real coffin of Elizabeth McAshton and Von Sackville-Bagg, but the amulet isn't there. Suddenly, Tony has another vision of Elizabeth burying the stone under the floorboards of her room...which is now Tony's room. Rudolph and Tony go to Tony's bedroom and start prying up the floorboards, but Rookery is wise to them. When Tony refuses to hand over the stone, Rookery takes Tony, stone and all, for a ride in his vampiremobile. As they drive along, they are attacked by a herd of flying vampire cows (the cows on which Rudolph and his family have been feeding) who cover Rookery's windshield with cowpies.Meanwhile, Frederick and Freda realize that tonight is the night that the Attamon comet will cross the moon, and all the vampires must be called to unite on the cliffs. Frederick is still too weak to fly, so they introduce themselves to Tony's parents and invite them to view the comet, too, using their car to drive out there. The entire vampire clan is gathered on the cliff, but where is the amulet? At the last minute, Rudolph and Tony fly in. Tony gives the amulet to Frederick who says the magic words. A red light descends from the comet, a red fog creeps over the vampires, and they all disappear.Epilogue: It is some weeks later. Tony and his parents are at the market in town when a new family moves in. It is the Sackville-Baggs, but they are human now. At first they don't recognize Tony, but a little whistle from Tony brings back their memories. [Original Synopsis by bj_kuehl.]