THE SCENE: Greendale Community College's biology classroom. THE CRIME: An innocent, unsuspecting yam, completely destroyed. Jeff, Annie and their professor are at the crime scene, surveying the damage of what used to be their final project: a yam about to sprout. But it appears as though overnight someone destroyed their project, and their chances at an A. Noting that it was an innocent mistake, the professor agrees to give them a passing grade for the efforts. But for Annie, a passing grade just isn't good enough. Determined to get an A, Annie vows to bring the perpetrator to justice.
A crime drama aficionado, Shirley takes control of the situation, ordering crime-fighting team Troy and Abed to get on the case. They've got 48 hours before the trail runs cold, so they better start with the last person to see that yam alive.
The main target is Todd; as Pierce wisely notes, who else would be intent on seeing the study group fail? A suspicious cut on his hand makes him a prime suspect, but Todd's story checks out. Todd claims the door was locked when he went to check on his yam that night... There's no way he was responsible.
That means they've got to track down the key and see who checked it out from administration the night of this dreadful crime. Fat Neil checks the books and reveals that Magnitude had the key that night. But Magnitude explains that his backpack was stolen with the key in it... there's no way it was him. Pop pop!
Troy and Abed set up a trap at the library hoping to catch their perpetrator, with Troy innocently leaving his backpack behind to see who swipes it. And the robber turns out to be none other than... Star-Burns! Star-Burns is caught red-handed by Troy and Abed, but he claims he has nothing to do with the yam incident.
Without any evidence, the team decides to get all the dirt on Star-Burns they can, breaking into his locker in hopes of some incriminating finds. When the locker opens, flasks and other lab equipment come pouring out; apparently Star Burns has been running a meth lab out of his van. He still swears that despite his transgressions he has nothing to do with the incident; in fact, he witnessed Todd drop the potato and make a run for it! Troy and Abed pinky swear to keep Star-Burns' secret as long as he agrees to testify at the trial of the smashed yam and tell the truth about Todd.
Todd's a decorated war veteran, and his officer uncle manages to scare Star-Burns out of testifying. But the team's determined that they still have a strong case and move forward as planned. At the trial of the smashed yam, Annie grills Todd into submission, ruthlessly scaring the poor guy into confessing to his crime. But Jeff notes that in Todd's confession, he said that he only dropped the yam because the jar was too hot. Something here doesn't add up.
Jeff's closing statement makes a shocking revelation. He approaches the yams and drops them on the floor one by one, and each yam smashes to pieces on immediate contact with the floor. No raw yam can do that... these yams have been cooked! And the projects sabotaged! Someone has been breaking into the bio room at night and pouring hot water into the jars. So the question is... whose yam ISN'T cooked?
Vicki's yam bounces right back when it hits the floor, but Vicki claims she's innocent. Fat Neil stands up and confesses; Vicki's yam never sprouted and he didn't want her to fail, so he threw off the grading curve. He wanted to make sure Vicki wouldn't have to go to summer school so they could finally have sex in his parent's cabin. It looks like in the end... it really was all about biology.
As the gang enjoys a glass of scotch and reflects on the day's events. they get a shocking call. Star-Burn's meth lab exploded... Star-Burns is dead.