A storybook prologue tells how the young Cinderellas father remarried after her mothers death to Lady Tremaine, who brought along her own daughters Anastasia and Drizella. They were kind to Cinderella at first, but after her father also died they revealed their true colors, taking over the house and treating her as a servant.
Cinderella is woken in the morning by Jaq, the leader of her mouse friends, who tells her a new mouse has been caught in a trap. She frees the new arrival and names him Gus, and Jaq takes up explaining to him how they survive in the house while avoiding Lady Tremaines cat Lucifer. The group launches an elaborate plan to swipe breakfast under Lucifers watch, which also involves Cinderellas dog Bruno who dreams every night of taking care of Lucifer.
In the nearby palace, the King despairs of his son seeming to have no interest in finding a wife, as hes getting old and wants to meet his grandchildren. He and the Grand Duke decide to force the issue by holding a grand ball with every eligible woman in the country required to attend. When the news comes to Cinderellas house, Lady Tremaine claims to agree she should come too, while actually scheming to work her so hard she wont have any time to put a formal gown together.
The mice decide to make the dress themselves, and surprise Cinderella with it on the very night of the ball. However, when she comes down to go with her stepfamily, they drop the whole act and Anastasia and Drizella violently rip the dress to pieces, leaving her sobbing as they head off to the palace. But she still retains enough hope to be visited by her Fairy Godmother, who magically makes her perfectly presentable with a coach made from a pumpkin, the mice as fancy stallions, and Bruno as the coachman, plus a fancy new gown and glass slippers. She sends Cinderella off with a warning that the magic will all wear off at midnight.
At the ball, the Prince is utterly bored as he greets each lady, and is especially not taken with Anastasia and Drizella. But just then Cinderella arrives and hes immediately drawn to her. They have a dance with Cinderella marveling at her new love for this man she doesnt even realize is the Prince. Shes ultimately so swept up that she loses track of time, and has to race away from any witnesses as the clock begins to strike midnight, in such a rush that one of the glass slippers is left behind, and they dont go back to normal like everything else.
The King is overjoyed to hear the Prince made an attachment with one of the guests, but then dismayed that all they have to go on is the slipper. The Grand Duke is promptly set out to find a woman whose foot fits it, and alerts the whole country to the search. When word reaches Cinderellas house, shes still in such a lovestruck daze that she starts reliving her dance, causing Lady Tremaine to realize who the woman who stole the Prince away from her daughters was. She locks Cinderella in the attic to keep her from trying the slipper.
When the Grand Duke arrives, Jaq and Gus get the key to the attic door from Lady Tremaines pocket and make the arduous trek up the stairs with it. But then Lucifer arrives and they have to fight for their lives, to which Cinderella alerts Bruno, who finally gets to fight his nemesis and ends up sending him out the window. The door is unlocked and Cinderella gets downstairs just as the Grand Duke is leaving, but Lady Tremaine makes one last spiteful move and trips him, causing him to drop the slipper so it shatters. But the despair is short-lived as Cinderella reveals she still has the other slipper, and she and the Prince are quickly married.