Els is a courier, a girl who takes Jewish children on the back of her bike to safety on farms in Friesland. When she leaves Isaak, disguised as Jan, at a farmhouse with kind people, he is miserable until he makes friends with a beautiful black horse, Hero, a Frisian wanted by the Germans. The first time the Germans come for the horse, Isaak comes up with a plan to save him, but the second time they come, Isaak can do nothing to protect the animal he loves.