Fierce: 'Electrifyingly suspenseful' Ashley Audrain, author of THE PUSH

Lincoln is a good boy. At the age of four, he is curious, clever and well behaved. He does as his mum says and knows what the rules are.

'The rules are different today. The rules are that we hide and do not let the man with the gun find us.'

When an ordinary day at the zoo turns into a nightmare, Joan finds herself trapped with her beloved son. She must summon all her strength, find unexpected courage and protect Lincoln at all costs – even if it means crossing the line between right and wrong; between humanity and animal instinct.

It's a line none of us would ever normally dream of crossing.

But sometimes the rules are different.