On the brink of World War II, a family is forced out of their London home and into the countryside. Wolfie and his older sister Dodo are devastated to leave behind everything they've ever known, but they slowly settle into their new life. One day they come across an orphaned foal, which they raise as Hero, a strong and beautiful horse who lives up to his name when he saves the children from a fire. Wolfie and Dodo find comfort in their new life, but the war is escalating quickly and horses are needed for combat. One night, Hero is stolen, and the children are shattered. Years go by and there's no sign of Hero returning. It's only when Wolfie becomes a stable hand that he discovers Hero has ended up working in the mines under terrible conditions. Then and there, Wolfie resolves to save Hero, even if it puts his own life in danger. Together, they will survive.