Evacuated from war-torn London, Cherry and her brothers are sent to live with their Aunt Jandie on a farm in faraway Tasmania. When Jandie is taken ill and sent to hospital, the children are left on the farm under the guardianship of nasty old Ma Pinner, who is disliked even by her own son Tas. The children rebel against Ma Pinner's harsh and spiteful treatment and escape to the secret cave they found while exploring the bush. They later uncover a plot by Ma Pinner to rob their aunt of her farm.