The illustration on the cover shows Count Nightwing briefly emerged from his coffin with dead flowers in his left hand and a bottle of Vampire Breath in front of his coffin.
Freddy Martinez is babysitting his neighbor Tyler Brown, and telling him a spooky story about how werewolves will come up behind you and breathe down your neck. Freddy climaxes his horrifying story, by ruthlessly tickling the poor child. Then Freddy turns to tickle his female best friend, Cara Simonetti, who came over to keep Freddy company. The two wrestle around and then Freddy talks some more about how creepy werewolves are. As Freddy talks about the soft thud of the werewolf's feet, the children hear a soft thud of footsteps from within the house. It is not really a werewolf at all, but Tyler's parents.
Back at Freddy's house, he and Cara pass the time by playing some air hockey in the basement. The game quickly devolves into an actual hockey match, as the two children punch and shove each other around the small room. Freddy pushes Cara into the wall and the two playfully wrestle each other. Eventually Cara accidentally knocks over the large china cabinet, revealing a hidden door. Behind the door, the two children discover a dark tunnel. Reasoning that if you find a secret door leading to a secret tunnel in your basement, you are required to investigate where it leads, the two children grab some flashlights and make their way down the damp stone tunnel.
At the end of the tunnel, they find a small room holding an empty coffin. Freddy picks up a small glass bottle inside the coffin and the two children struggle to read the label on the bottle: "Vampire Breath." The two children fight over opening the glass bottle, leading them to drop the container. The bottle spills open, spewing out noxious smoke.
As the smoke clears, the two children spy a form inside the coffin: an old man! The bald ghoul blinks his eyes awake and slowly climbs out of the coffin. He announces that he is Count Nightwing, a prominent vampire, and he is very thirsty. The vampire chases the two children down the tunnel, trapping them at the end when the entry door swings shut. Freddy figures ladies first and lets Count Nightwing attack his friend first. But Nightwing quickly recoils from Cara's neck, after he realizes he does not have his fangs. Count Nightwing gets furious and makes the children help him look for the bottle of Vampire Breath they opened.
The Vampire Breath is a magical potion that brought Count Nightwing into the future from his own time, and if the children help him find the bottle, he will go back to his time and leave them alone. Eventually they find and open the bottle, but the two children are more than a little miffed to discover that they have been brought back in time with Count Nightwing. Once the fumes fade away, Cara and Freddy find themselves in a large room inside what appears to be a castle. At the top of the high ceiling, yellow moonlight pours in, revealing dozens of coffins. Freddy and Cara hide in the shadows, as dozens of vampires emerge from their coffins, turn into bats, and then fly out through the open windows.
The two children try to escape, only to run into Count Nightwing, who is awfully sorry about transporting them back to his time. He tells the children he would be happy to help them by turning them into vampires. Freddy and Cara decline the generous offer, but Count Nightwing is insistent that the two help him find his bottle of Vampire Breath. See, the empty bottle was empty in 1996, but in 1896, it's full of Vampire Breath.
Count Nightwing explains that every vampire must supplement their diet of blood with daily doses of Vampire Breath. A vampire's private dose of Vampire Breath is highly guarded and kept hidden from the other vampires, only Count Nightwing can't remember where he hid his bottle or his fangs. The count forces the children to help him look around the castle for the potion. Freddy and Cara split from the count and reason that if they find his bottle of Vampire Breath first, they can use it to zap themselves back to the future.
Cara has an even better idea: leave the vampire castle. Unfortunately, all of the windows are either too high or outfitted with black bars to prevent thieves from stealing the Vampire Breath. As the two children walk through a vast dining room covered in dust, Cara gets an idea. Cara figures that since the vampires don't eat, they would have no need for the kitchen, so they can hide out there and figure out their next move. Cara is quite insistent on not becoming a vampire. Inside the kitchen, they spot a window without bars! Freddy jumps up on the ledge and prepares to jump out when he notices his feet are not making contact with the ground. He looks down and sees that the castle is built high atop a cliff. Freddy is saved from falling to his death by a giant bat, which swoops him up back into the kitchen. The man bat transforms back into Count Nightwing, who chides the children on trying to escape and tells them to get back to work looking for his bottle. The children keep checking room after room in the cavernous castle. Finally they come across another mausoleum lined with empty coffins-- except for one with its lid clamped firmly shut. Inside a hidden pocket in the coffin they find the bottle of Vampire Breath. Before they can make their escape, the two are stopped by a twelve-year-old girl with curly blonde hair. She introduces herself as Gwendolyn. Then she explains that Count Nightwing and the other vampires keep her prisoner in the castle, forcing her to clean their coffins under the threat of turning her into a vampire. Gwendolyn leads the children down a secret passageway in the castle, so they can escape and be spared her ordeal. Once she gets the children deep within the castle walls, the blonde girl reveals her fangs and attempts to feast on the two friends.
Before Gwendolyn can sink her teeth into Freddy's neck, Count Nightwing, shows up and the twelve-year-old vampire girl and the old man vampire duke it out. Freddy and Cara quietly slink out of the passageway and find themselves in a supply closet loaded with empty bottles of Vampire Breath. Count Nightwing shows up and thanks the children for reminding him where he hid his full bottle: among the empties in the closet. As Nightwing furiously searches for his bottle among the spent vessels, the two children find it first. But then Count Nightwing swipes it. But then Cara swipes it back and the two children play Monkey in the Middle with the vampire. Their game goes back and forth over the vampire's head, until Count Nightwing simply floats up in the air and grabs the bottle. Only that bottle too is empty, as Freddy made a switch.
Freddy opens the bottle of Vampire Breath and is relieved to see his air hockey table through the thinning smoke. He and Cara are however not relieved to see Count Nightwing came back with them. Nightwing pouts around the basement and complains that he still does not have his fangs and he will starve to death without them. Just then, Freddy's parents barge down the basement stairs. Freddy tells them the old man is a real-life vampire. Freddy's mother tells him to go upstairs to make a sandwich for himself and Cara, because the vampire, Count Nightwing is Freddy's grandfather, who was taking a nap. Freddy's mother tells the old man that his fangs are safe, floating in a glass in the secret basement bathroom. Freddy is surprised that not only does he have a grandfather he never knew about, he has a vampire grandfather that his parents kept buried in a secret passageway behind the china cabinet.
This would also make him a vampire as well, but he doesn't get his fangs until he's a hundred years older. Freddy and Cara sneak off to the hidden basement bathroom and lock themselves inside. Soon, before the two begin wrestling again, Cara discovers a bottle marked "Werewolf Sweat.” Cara spills the bottle over the both of them and they begin to loudly growl.
- Their family name is a reference to the butler from Dracula.
- Freddy's mother was mentioned by name in the book: Cynthia Martinez.