Matthew's parents are worried. At eleven, he's much too old to have an imaginary friend, yet they find him talking to and arguing with a presence that even he admits is not physically there. This presence - Chocky - causes Matthew to ask difficult questions and say startling things. Who is Chocky? And what could it want with a 11-year-old boy?

David Strorm's father doesn't approve of Angus Morton's unusually large horses, calling them blasphemies against nature. Little does he realise that his own son, and his son's cousin Rosalind and their friends, have their own secret abberation which would label them as mutants.

Gus the clown is Peter and Santa's only living relative, and escape to the circus seems a better idea to them than an orphanage. But Gus will keep the children only if they make themselves useful - and they have to fight hard to really belong to the circus.