Myrtle Meek has everything a girl could want, and it is never enough. Her parents, Christopher and Maureen, are gentle, devoted librarians who have never once said no to her. So, when her twelfth birthday comes round and there is nothing left on her list, Myrtle makes her boldest demand yet; "I want a Fing!" Nobody knows what a Fing is, but her parents agree anyway, and Christopher sets off across oceans to the lost jungle where this rarest of creatures is said to live. He is not the only one hunting it. The vain Viscount, self-proclaimed world's greatest animal expert and deep in debt to the bank, needs a Fing for his wildlife park, and sends his long-suffering Nanny to get one by any means necessary.

The Fing that finally arrives at the Meeks' house is bad-tempered and gleefully destructive: the world's worst pet, and every bit as mischievous as Myrtle herself. After a disastrous start, the two become unlikely friends, and the Fing even follows her to school, much to the headmaster's horror. But the Viscount is closing in. Brought to life by puppeteers, with Taika Waititi as the villain, this cheeky, big-hearted family adventure discovers that the only thing worse than not getting what you want is losing what you had.