Despite the title, this family film is far from being happy. Mother, Emma (Emily Watson) has a bookstore to bankruptcy, father, Frank (Nick Frost), is completely exhausted by work, daughter, Fay (Jessica Brown Findlay), walk through that difficult period typical of adolescence and spades exams, and his son, Max, is too smart for his own good, so that’s bullied at school. It’s no wonder, then, that they are fighting all the time! And, as though it were not enough, the four arrive at a party Halloween, dressed in costumes specific to the holidays, but instead spend, are cursed by a wicked witch named Baba Yaga (Catherine Tate ). In an instant, their costumes become reality, and Emma is a vampire, Fay, a mummy bandaged from head to toe, Max is a little hairy werewolf, and Frank is, of course, Frankenstein’s monster. The family now sees forced to unite to be able to find the witch and an order to break the spell.