It's been 6 months since the portal was linked between Earth and Equestria was created and every since then humans and ponies are living in peace. Now in Ponyville Equestria one if the most peaceful town hold a serial killer with already had three ponies killed and he/she won't stop untill he/she is caught. Since the Equestrian never handled murder before Princess Celestia calls the humans off assistance and the send in the BAU (behavior analysis unit)