A storm in Ponyville drives Applejack and Rarity to seek shelter at Twilight's. Twilight is alone since Spike is in Canterlot on "royal business" and she uses this opportunity to host her first slumber party. Unfortunately, all throughout the night Rarity and Applejack butt heads, starting with dissenting views about the makeovers that start the night's activities. During the ghost stories, Rarity and Applejack suggest stories that allude to why they don't like each other. The lights go out and Twilight Sparkle tells the tale of The Headless Horse, which is a play on the story The Headless Horseman, succeeding in scaring both Rarity and Applejack. They continue to clash when they move on to making s'mores. And when they play truth or dare, they use it against each other; Applejack daring Rarity to get her mane all wet and ruined, Rarity daring Applejack to dress in a ridiculous gown, eventually they wind up just yelling at each other. Sensing conflict, Twilight Sparkle tries to keep things moving to avoid escalation, unfortunately what she suggests is a pillow fight, which in no time turns into an all-out pillow war between Rarity and Applejack. Twilight Sparkle, thoroughly bombarded by pillows, suggests that they just go to bed.
Their petty arguing and fighting continue even when the ponies try to go to bed. At this point, Twilight Sparkle interrupts their bickering, upset that her friends are fighting too much to have any fun, hence ruining her slumber party. Just as Twilight Sparkle asks if there is "anything else that can possibly go wrong", a nearby tree is hit by lightning and begins to topple towards a neighboring house. Applejack, not heeding a warning from Rarity, lassos the falling tree and instead of stabilizing it, sends it crashing through Twilight's bedroom window. Rarity focuses on cleaning up the mess of books, and Applejack tries to push the tree back out of the window while Twilight Sparkle desperately searches through her slumber party book for a section on dealing with fallen trees in the middle of the bedroom. When Applejack fails to move the tree out on her own, she eventually apologizes to Rarity about her habit of attention to detail and convinces her to focus on helping her with the bigger task instead, and not worry about getting her hooves dirty. Rarity uses her unicorn magic to turn the tree top into tiny bush sculptures, clearing the house at the price of getting dirt all over her; Applejack then proceeded to gently toss the broken trunk out the window.
With the storm (and their differences) finally settled, Applejack, Rarity and Twilight Sparkle are finally able have fun. In the end, Twilight Sparkle officially declares the slumber party a success. She suggests another slumber party the following night but gets a pillow thrown in her face. The episode closes as the sky clears up, revealing a bright sunny day.