Presented like an episode of Law & Order (1990), the study group attempts to find out who squashed their biology project: a yam. Troy and Abed become detectives, Shirley is their boss, Jeff and Annie pose as prosecuting attorneys, while Pierce is an informant and Britta a lab tech.
In a "Law and Order" opening, two janitors discover a -- gasp! -- yam has fallen from a lab table to its death. Or has it been murdered? That's the question Annie wants answered. Though it is the middle of the night, she has summoned Jeff and Marshall to the scene of the crime. "Our final project has been destroyed!" Annie says. "That was going to be an A-plus yam!" Marshall tells Annie that she and Jeff will receive a "passing grade," which isn't enough for Annie, who wants the top grade. "Now if you'll excuse me, I was watching 'Mama's Family,'" an annoyed Marshall says before exiting.
Shirley, Abed and Troy then enter -- and Annie enlists them in the investigation, reasoning that Marshall will give them an A if they solve the case. The next day, Pierce oversees the betting on an elderly arm wrestling tournament when the yam investigators enter. "Youth!" yells a contestant. "Scatter!" Pierce confesses that he forgot to water the yam and, by the time he arrived at the lab, the door was locked (his excuse: "I feel asleep in a sunbeam"). "You should be talking to someone who wants to hurt us: Todd!"
So Abed and Troy confront Todd, who also claims that the lab door was locked when he got there. "Lot of that going around," sneers Troy. The investigators soon figure out that the lab door gets locked at 8 p.m. Whoever got into the lab would have needed a key. So it's off to the office, where Fat Neil checks his records -- simultaneously expressing his condolences for the yam -- before revealing that a key to the lab was checked out by ... Magnitude. Magnitude, we learn, went to the library with the key in his book bag before the key was stolen. "Only one way to catch a dirtbag like that," Abed says.
Moments later, Troy sits at a library table "in disguise" as a student (complete with letterman's sweater). He announces that it's time to visit the restroom, leaving his book bag behind. Star-Burns appears from behind a stack of books and snags the bag. He is confronted by Abed and Troy and is soon in a dark room being questioned. Abed and Troy play good cop-bad cop. How do we know? "He's the bad cop, I'm the good cop," Abed says. "You can trust me.
But Star-Burns won't fall for such an the obvious trick (surprisingly) so Abed and Troy head to the morgue. Rather, they head back to the lab where a teacher has done an autopsy and explains that "this level of smooshing is consistent with someone stepping on the yam after it was dropped," she says. Later, Jeff suggests breaking into Star-Burns locker and finding dirt on the weirdo to use as leverage. He tells his fellow investigators not to get soft. So Abed and Troy break into the locker and discover a biology test tube. "Clean up on aisle busted," Troy says. Star-Burns then rounds the corner, sees the investigator ... and flees. A not-so-furious chase ensues.
Finally, Abed and Troy catch up with Star-Burns who explains that he stole the lab equipment only so he could build a meth lab in the trunk of his car. Star-Burns then claims that he saw Todd do the deed. During the next biology class, Jeff and Annie rise to present their case to Marshall, accusing Todd. Suddenly, the door opens and a man in uniform enters. It's Commander Archwood, who had the pleasure of leading Todd in Iraq. Archwood is staying on Todd's couch for the weekend because he's in town for a wedding -- and he won't stand for his former soldier being harassed.
Soon, both legal teams are in Craig's office (chambers?). "All you have is the word of this Mr. Star-Burns," says Archwood. And what was Star-Burns doing in the lab when he supposedly saw Todd? Jeff refuses to answer, explaining that the information is protected under a pinkie swear. Marshall steps forward, defending Jeff and Annie's right to prosecute and getting in Archwood's grill (In this conversation, Marshall Kane says, "A man's got to have a code," a nod to Omar from The Wire also played by Michael K. Williams. Dean Craig exclaims, "Awesome," after the reference). It all makes Craig very, very excited. Later, Jeff and Annie work into the wee hours of the afternoon on their case. Chinese takeout litters the lab. Abed and Troy enter with bad news: Archwood threatened Star-Burns, who has fled. The team's only witness is long gone. They have no case.
But will that stop justice? Not if Annie has anything to say about it (and she does, of course). Soon, the case/class begins. Todd is put on the witness stand (folding chair) in full uniform and denies the charges against him. Annie, wearing a smart business suit, attacks Todd, laying out his motive: his own yam that wouldn't bloom. "Did you kill our yam to settle the score?!" she demands. "Did stomping on its roots make you feel like a big man?!" Todd crumbles. "It was an accident!" he exclaims. Todd says he picked up the yam to look at it and was burned. He then dropped the yam. Annie breaks out into an awkward celebratory dance. Jeff then asks for a sidebar in Marshall's office.
Inside the office, Jeff urges Marshall to drop the case and give both his group and Todd a C. Annie is horrified. "A man has to have a code," explains Jeff, using the very words Marshall used earlier when confronting Archwood. "I can only assume there has to be a female equivalent to that -- a code-ette or something ... An innocent man might get an F." Back in class, Jeff stands for his closing argument. He goes to the yams, dropping each on the floor to the gasps of the class. When they hit the floor, they smoosh. Jeff explains that someone has been boiling the water the yams rest in at night -- making them extra smooshy (and thus, appearing to have been stomped on when dropped).
But one jar contains a yam that doesn't smoosh on contact with the ground. One jar contains water that hasn't been boiled. That jar belongs to Vicki, who is horrified at the accusation. Fat Neil then stands. "I boiled the yams!" he confesses. "Vicki's yam hadn't sprouted and I didn't want her to fail so I threw off the grading curve so she didn't have to go to summer school and we could finally have sex in my parents' cabin." Fair enough. Yells Marshall: "Holy crap! We are definitely dissecting pine cones next year!" Later, Jeff and Annie relax in Marshall's office when he gets a call. The meth lab in Star-Burns car has exploded. "He's dead," Marshall says.
The episode ends with a special thanks to Dick Wolf.