Ms. Barch assigns as a science project the task of training a mouse, using positive or negative reinforcement, to run a maze. She puts Daria with Kevin, which horrifies Brittany. Brittany, however, gets an even worse shock when her partner turns out to be Upchuck, though he’s overjoyed.

Daria easily figures out that Kevin won’t bother her while she’s working on the maze if she turns on the Pigskin Channel, though he does still wander around sometimes (during halftime) and break stuff. Quinn, of course, sees this as a perfect opportunity to hook up with the most popular guy in school, so she continually flirts with him and cooks for him. Jake inevitably tries his male-bonding techniques on his new couch-mate, though Kevin’s usually too into the game (or too stupid) to respond.

Meanwhile, Upchuck has succeeded in making Brittany absolutely miserable. He blackmails her with a picture of her making out with the quarterback of Lawndale’s main rival team, and she has to do whatever he tells her to. She’s also growing increasingly suspicious about both of the Morgendorffer sisters’ intentions with “her” Kevin. So, using the twisted logic of the stupid, she comes up with a plan to get her boyfriend back from the “Morgendorffer temptresses.” She kidnaps Daria’s lab mouse and gives it to her evil little brother so that the science project would come to a halt and Kevin would have no excuse to go to the Morgendorffer house.

After the kidnapping, Daria figures out who stole the mouse and why pretty quickly, so she negotiates an agreement with Brittany: the mouse for Kevin.

However, the poor thing is so terrified from getting tortured by Brittany’s brother that all it will do is lie in a corner of the maze and shiver fearfully. When Daria explains this to Ms. Barch, it’s made obvious that she did the experiment and Kevin didn’t, so Ms. Barch gives Daria an “A”. Kevin, who’s quite easy to please, is also happy with his grade, a “D”.