When Ivy Sparrow's grandmother Sylvie is rushed to hospital on Christmas Eve, Ivy and her annoying big brother Seb cannot imagine what lies in store for them. For Sylvie's house has been ransacked by unknown intruders, a mysterious feather writes bizarre warnings in midair, and a very strange policeman suddenly arrives at the door waving ...a toilet brush. Ivy and Seb take the only escape on offer and suddenly they find themselves in the incredible world of Lundinor, a city beneath London where uncommon people live and trade in uncommon goods. A belt that enables the wearer to fly. A yo-yo that turns into a weapon. With Seb arrested, Ivy must rescue him - but in doing so, she discovers a family secret as shameful as it is incredible, and realizes that there is much more to eccentric Grandma Sylvie than anyone could have guessed. With the forces of the evil Dirge closing in fast, and with a terrifying uncommon alarm clock whose hands point to the deaths of all her family, Ivy must find a way to save them all before it's too late.