In 1935 London, widower Michael Banks lives in his childhood home with Annabel, John, and Georgie, while Ellen and Jane are helping him to raise the children. However, Michael has taken a loan from the Fidelity Fiduciary Bank to cover expenses, and William Weatherall Wilkins sends his associates to warn him his house will be repossessed if the loan is not repaid entirely by Friday. Michael and Jane remember George left them shares in the bank that can cover the loan, and search the house for the certificate proving their ownership of the shares. During the search, Michael finds a kite, but finds no worth in it anymore and puts it out to give away. While out in the park with Annabel and John, Georgie finds the kite and tries flying it. He ends up being almost pulled into the sky, but then Mary Poppins comes down, decides to take care of the three children as their nanny, and starts off by drawing them a bath, which leads down to an oceanic world; however, Mary Poppins denies anything fantastical happened. Michael goes to the bank to see if he can find proof of his shares, but Wilkins denies there are any records of them before tearing the record out of the official ledger and burning it in the fireplace. That evening, Annabel and John decide to sell their mother's "priceless" bowl to pay off the debt. Georgie tries to stop them, and the bowl ends up damaged while the three were fighting over it. Jack greets Mary Poppins and joins her and the children on a trip inside the painting on the side of the bowl. The group meets the talking animals drawn on the bowl, and Mary Poppins creates the Royal Doulton Music Hall. However, Georgie is kidnapped by a wolf, weasel, and badger, who try to steal the children's stuff, and Annabel and John go to rescue him. They successfully do so but end up going out of the painting, and later wake up in their beds, thinking their experience was a dream but realizing it was shared. The next day, Mary Poppins and the children go to see Topsy to get the bowl fixed, and find out the bowl has little monetary value. They then go to the bank to give Michael his briefcase, but when the children go to Wilkins' office to ask him for help, they overhear him planning to take away their house. Realizing Wilkins and his associates turn out to be also the same animal gang who kidnapped him, Georgie interrupts the banker's meeting. When Michael arrives, he does not believe the children and becomes angry with them for putting the house and his job at risk. Mary Poppins takes the children home, and they are guided by Jack and his fellow lamplighters, who teach the children their lingo. Back home, Michael scolds his children for putting his job at risk, telling them the bank repossessing the house is true, and fears he will lose his wife’s spirit too, but he ultimately forgives them after they comfort him with Mary's advice that their mother is always with them. The Banks family prepares to move out of their house, but while examining his old kite, Michael realizes Georgie used parts of the shares certificate to cover the kite's holes. Michael and Jane head to the bank while Mary Poppins and the children go with Jack and the lamplighters to Big Ben to "turn back time." After scaling the clock tower, Jack and Mary turn Big Ben back five minutes, giving Michael and Jane enough time to reach the bank. Michael and Jane reach the bank in time, but are unsuccessful in getting their shares due to not having the part with the signatures on the certificates. However, Mr. Dawes Jr. arrives and fires Wilkins from the bank for his corrupt business practices, then reveals George had invested Michael's tuppence from 25 years ago. The next day, the Banks family goes to the park and purchases balloons that take them into the air, in which they are joined by Jack and numerous others. When they return home, Mary Poppins realizes it is time for her to go, and Michael and Jane thank her as she flies back up into the sky.
