Princess Celestia was enraged when Princess Luna tried to keep Equestria at night for a day. This matter led to hatred between the two sisters, and they declared war against each other. Celestia took to tearing the Elements of Harmony apart. Twilight Sparkle, Apple Jack and Rarity were on her side. Pinkie Pie, Rainbow Dash and Fluttershy were on Luna's side.
Rainbow Dash's loyalty was pulled apart. She decided not to be loyal to anypony, anymore.
Her element was revived when she was sent on a mission from Luna. Luna wanted her to go to The Plains, a dangerous place, where a certain spell book was believed to be there. Rainbow Dash met an enemy of great power while on her journey.
Rainbow wanted to kill him at once, but when he stated the reason why he wanted to work with her in the meantime, and kill each other later, she agreed. After all, it was better to have a companion when you're in The Plains.
Rainbow Dash and her foe had to face several traps, sandstorms and manticores roaming freely in The Plains - not to mention their growing romantic tension...
After the Journey, Rainbow Dash and her companion sets out to stop the three-year war.