-There is a criminal loose in Greendale: the Ass Crack Bandit.

-The ACB's m.o. is to drop a coin down into someone's butt crack while they are bent over.

-The ACB has been attacking students all over campus, and Dean Pelton convenes the study group, along with Professor Duncan (John Oliver) and Professor Hickey (Jonathan Banks), to help draw up a profile.

-The gang--Annie and Jeff, in particular--track the ACB, and come close to apprehending him many times.

-Annie believes the culprit is a teacher, and Jeff believes (based on his letters) that the ACB loves the Dave Matthews Band.

-After a phone call from the ACB, Annie, Jeff, and Dean Pelton run to the campus stables, where they discover Star Burns, who they had believed to be dead.

-Star Burns is officially presented as the ACB, even though Annie and Jeff have their doubts.

-When encountering Professor Duncan at a party after Star Burns's arrest, Annie comes to believe that he is the ACB--because he has a roll of quarters, loves Dave Matthews, and encourages her to pick up her keys in front of him after she drops them.

-But soon after Annie escapes, Professor Duncan himself becomes the ACB's next victim.

-Star Burns reveals to Jeff that he is not the ACB, and only agreed to admit to the crimes because Dean Pelton promised to buy him a space heater.

-Annie and Jeff give the real ACB chase, but then run into Shirley, who tells them that Pierce has died.

-The real ACB is never officially apprehended.