Spectrum Analysis is an ace detective from Manehatten, and his assistant Eye Spy still has some work to do. They both are in for the case of their lives, when the mayor of Ponyville calls them in because a criminal known as the "Cutie Mark Killer" is striking down on innocent ponies. Every Monday morning, a picture of a cutie mark is hung on the town hall door, and by Sunday evening the bearer is dead.
Spectrum and Eye team up with bearers of the Elements of Harmony to take down this villain. The only problem is that they have no idea who it is. The killer seems to leave no trace of evidence behind.
Will Spectrum and his friends stop the Cutie Mark Killer in time?