I did have a bit of trouble when I first started reading it though. The book was referring to Queen Chrysalis, who was recently defeated. I thought that maybe this was a later volume in the series as a result. But no it isn't.
The story starts out with the Cutie Mark Crusaders (the little sisters of three of the main ponies who are trying to find their flank markings) getting kidnapped by Queen Chrysalis. The next day, the main ponies realize something is weird about all the people in Ponyville (and that the three younger ponies are acting extremely weird, too). Recognizing the other ponies to be changelings brought on by Queen Chrysalis, they set out to rescue their town. Unfortunately, the three little ponies are missing. Queen Chrysalis gives our heroes three days to reach them before she destroys them.
|The Zombie Walking Incident