A new girl, Sara Beth, arrives at school. She is unresponsive when the other children try to befriend her.
Becky decides there must be something more to the situation than Sara Beth simply being shy. She begins to look for clues.
Becky checks out Sara Beth's shabby clothes, her schoolwork, her tendency to take home items she's not supposed to. But the biggest clue comes when Becky observes that Sara Beth loves taking care of the class guinea pigs one day and is deathly scared of them the next.
There could be only one explanation: Sara Beth is actually twins named Sara and Beth who take turns coming to school. Why, you ask? The parents could only afford one winter coat and thought this was the best solution.
The girls tell the teacher, and learn that there is a whole stash of winter clothing stored away for just such a purpose. The end.