Underclassman Trailer (2005)

Tre Stokes is a 23-year old undercover cop and goes to Westberry High to figure out the death of a student. He befriends Rob Donovan and soon figures out that he has been stealing the cars at parties. Near the end, it is revealed that the principal of the school had been blackmailing Donovan, and was ringmaster of the crimes. After being kicked off the force by his father-figure police chief, Tray solves the case and is reinstated.