The film begins in Transylvania, where Count Dracula (Jason Isaacs) laments about his loneliness with his three bat servants. Suddenly, he receives a phone call via cellphone from Emma Wishbone (Emily Watson), who has mistakenly called him instead of a monster costume store. Rotten luck bedevils Emma until she reaches her bookstore, where she complains to her co-worker, Cheyenne (Celia Imrie), of all the troubles plaguing her family: Her own bookstore is in dire financial straits. Her son, Max (Ethan Rouse), is bullied in school and is a social outcast due to his nerdy mannerisms. Her daughter, Fay (Jessica Brown Findlay), is sarcastic and rude, caring only about boys. Her husband, Frank (Nick Frost), is constantly overworked and sleep deprived.Seeking to foster a sense of family, Emma makes a handful of monster costumes for her family - her as a vampire, Frank as Frankenstein's monster, Fay as a mummy, and Max as a werewolf - to wear to a monster-themed costume party presented by Cheyenne. Though the family is clearly not in the mood for such an outing, they nevertheless reach their destination. They unexpectedly receive a star treatment, only to discover that they have been mistaken for a monster-themed rock-and-roll band that was meant to perform at the party. Security deposits the family into the alleyway behind the building, where Emma finally snaps.The bad evening only grows worse when Baba Yaga (Catherine Tate) arrives to turn Emma into a vampire with a Transformative curse. The spell works, but unexpectedly turns the rest of the family into the monsters they were portraying. Enraged, Emma chases down Baba Yaga while her family splits up to visit various spots around the city. Fay goes to her crush's house, only to be rejected due to her appearance, while Max stalks and scares the school bully. Emma eventually captures Baba Yaga and demands to have her family returned to normal, only to discover the old witch's amulet - the source of her power - has worn out and must be recharged at the London Eye.After Baba Yaga escapes, the Wishbone family regroups at home, and they realize they must catch the witch to return to normal. The Wishbones reach the airport, with help from Cheyenne - who is unafraid of the Wishbones' new appearance. Fay manages to get them on the plane after learning she can hypnotize people, which she does with abandon. On board the flight, Emma begins to spiral into the more violent side of Vampirism as her blood-lust kicks in, and she attempts to bite one of her fellow passengers. A timely intervention from Dracula halts this, and he absconds with the confused and blood-hungry Emma aboard his personal jet, leaving her family on the passenger plane.As her family wonders where she is, Dracula tries to talk Emma into running away with him. She initially considers, due to not being happy with the issues with her family, but when she refuses, Dracula unceremoniously tosses her from his jet. As Emma regroups with her family by the London Eye, Dracula gets upset and tells his hunchback servant, Renfield (Ewan Bailey), to prepare his snowflake machine to destroy the world in retaliation.Meanwhile, Baba Yaga gets her amulet charged, and when Emma confronts her and tries to take the amulet, Baba sends the family to Egypt. Cheyenne tries to help, but she ends up befriending and helping Baba Yaga. She tells Cheyenne about Dracula's plan to turn Emma into a monster. Baba Yaga also tells her about how he imprisoned her and said he would free her if she did what he asked, and that the only way for them to return to normal was to be happy as themselves despite their appearance.Emma and the family hallucinate an Oasis while in the deserts of Egypt, but soon snap out of it and realize that they have been unknowingly walking in a circle. Dracula shows off the snowflake's power to his servant and swears revenge on the humans.Meanwhile, in Egypt, Max and Fay get angry at Emma, and go off on their own in separate directions. Emma then gets angry at her husband and pushes him away. Dracula had been watching her, and seeing this, goes to get her as she wanders around until the blood-lust finally takes over. She attacks a couple of tourists, but Dracula narrowly saves them and takes her away to his castle.Meanwhile, Frank comes across a stranded Jeep filled with models, and Fay meets Imhotep. Imhotep tells Fay she's pretty and shows her how to use her powers to become a sandstorm. Max gets mistaken for a piece of food by a camel, and he chases it to a desert hotel with glass pyramids, where Frank also happens to be. Dracula seeks to romance Emma in his castle. They dance, and though she refuses his advances at first, she eventually agrees to stay. After being shown to her beautiful new room, Emma realizes she misses her family. Cheyenne and Baba Yaga then suddenly appear and explain the truth about what Dracula had done to Baba Yaga.Frank, Fay, and Max separately come to realize that their newfound luck doesn't compare to when they are together as a family (Fay when she learns Imhotep plans to take over the world, Max when he learns that having people scared of you isn't very fun, and Frank learns to be a better husband). Baba Yaga and Cheyenne then transport them to Dracula's castle.Renfield tells them that if Emma doesn't marry Dracula, he will shoot a magical snowflake into the sun, causing all life on earth to die - except for vampires, as they don't require sunlight. The family confronts Dracula, with the intention of pouring homemade holy water in his bath. Though they lose initially, they eventually turn themselves human by realizing their love and need for each other and becoming happy. They then gain the upper hand by exposing Dracula to sunlight, and permanently freezing him with his snowflake.The Wishbones return home, and their circumstances change; Frank stands up for himself at work after putting a photo of their family adventure with the frozen Dracula on his desk, Max stops getting bullied, and Fay meets a nerdy guy in a knight's costume at a costume party that Emma throws at home. Baba Yaga, Renfield, and the three bats crash the party. The family takes another photo together, showing their happiness.