The plot could be about Margalo 2 getting lost and Stuart Little finding her. Stuart then helps her get back home. Along the way, they meet other animals who either help or hinder them. For example, a sly fox might try to trick them into going the wrong way, but a kind deer could show them the right path.
Maybe in the fanfiction, Stuart Little and Margalo 2 team up to stop an evil plan. There is a group of rats that are planning to take over the little mouse and bird community. Stuart and Margalo 2 use their wits and skills. Stuart is good at sneaking around and Margalo 2 can fly and spy. They gather other small animals like squirrels and chipmunks to form an army and fight against the rats. In the end, they succeed and their community is safe again.
A possible plot could be that Margalo 2 is on a quest to find a special object that can save her family. She enlists Stuart Little's help. They travel across different landscapes, from the city sewers to the rooftops. Along the journey, they face their own fears. Stuart has to overcome his fear of heights when they have to fly on Margalo 2's back to cross a large gap. They also have some heart - to - heart conversations, which deepens their friendship. Eventually, they find the object and Margalo 2's family is saved.