River's life is blown apart when his mum invites her new boyfriend into their home and their lives. River is instantly suspicious of Jason. He seems fake, too good to be true.

At school, River's routine fibs are escalating into something more serious, and his teacher gives him a notebook in the hope he can channel his fantasies into creative writing instead. And so, River begins The Liar's Handbook, and an investigation into Jason.

But what he uncovers is a terrible deception involving his biological father, the police force and his mum's environmental campaign group... but will anyone take his findings seriously?