A group of zebras comes to town, and knowing Zecora the ponies aren't afraid of them. They're rude, dishonest and mean, but ponies try to give them some leeway because after all, they just came from another culture and if Zecora is a well-adjusted member of the society then they can be too.
The zebras gets more and more rude and shameless, and while grumbling dissidence grows among the ponies no one dares say anything because they don't want to offend Zecora. This has the unintended consequence of raising resentment towards her too, as the ponies unwittingly pigeonhole her as "one of them".
Finally, Zecora herself stands up against them, and with her the ponies dare to speak their minds too. Together they drive the new zebras back where they came from, and learn a valuable lesson about why positive discrimination is as unjust as the negative.