After Mary Poppins departed London, Jane and Michael Banks grew up into loving and responsible adults. When Michael becomes a single father of three children after the death of his wife, Mary Poppins revisits the Cherry Tree Lane home again to try to help Michael and his family cope and move beyond their grief. Time passes quickly for most normal mortals. Mary Poppins has never been normal. Although it's now the 1930s, she looks exactly the same....

After a banker's children lose their nanny due to their misbehavior, a change in the wind blows in a magical nanny who matches the children's qualifications, but not those of their very proper father. As Mary Poppins helps the children magically explore the world around them, their father grows increasingly disapproving of her methods, and he must eventually deal with his own distance from his children.