Dame Sister Mary Leo was short in stature but a giant in training some of the world's most famous opera singers. This TV One documentary covers her early life as a fun-loving woman, who at the age of 28, joined the Sisters of Mercy, dedicating her life to the Catholic faith. Sister Mary took on a teaching role and turned St Mary's College in Auckland into a hotbed of operatic talent. Former pupils discuss her exacting methods and her fascinating mix of steel and compassion. Dames Kiri Te Kanawa and Malvina Major are interviewed extensively about their first formative singing teacher.