It's 1978, and Jack Sheffield begins his second year as headmaster of a small village primary school in North Yorkshire. There are three letters on his desk - one makes him smile, one makes him sad and one is destined to change his life forever. This is from nine-year-old Sebastian, suffering from leukaemia in the local hospital, who writes a heartbreaking letter addressed to 'Mister Teacher'. Jack tries to help, and so begins a journey through...