On the brink of World War II, a family forced out of their London home flees to the country. Wolfie and his older sister, Dodo, are devastated to leave behind everything they've ever known, but they begin settling into their new life.

One day they come across an orphaned foul, 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 then pass without any indication Hero will return. 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, a plan that places both of their lives in jeopardy. Together again, can they will survive?