Rainbow hears that Trixie is back in town, and that Twilight knows about it, but failed to tell her friends. Thinking something's up, she gets AJ to help her spy on Twilight, for her own good of course, and uses something she got from a purple unicorn stallion that had come to town a few days ago to help with the spying. Of course, things aren't way they seem with this, and the pair end up in more trouble than they expect, though hopefully not more than they can get out of.
(Vore Story, If you're not interested in that, Second Chapter is just Twilight and Trixie bonding. Inspired by the banner here on FiMFiction)