The twins Cloudchaser and Flitter love foalsitting Rumble together. After all, two mares are better than one. But one day, Flitter comes down with the horsey hives and has to spend the day at Ponyville Hospital. Therefore, Cloudchaser decides to find somepony else to foalsit with her. Derpy turns out to be the only pegasus mare available for the job. How many things could go wrong? A lot, as it turns out.