Two teenagers, Shockley and Goddard, come to the Psych office to hire Shawn and Gus for a case. They need help and the police won't take them seriously since they are kids. One of their teachers at the Meitner School for gifted students has killed someone and in two days, he'll kill again. The problem is, they don't know which teacher it is, who he killed or who his next victim will be. When they broke into school late one night to pull a prank, they accidentally hacked into a cell phone call being made from the campus. The only other information they could get is that the killer has a deep voice and a cousin named Muriel.
At the police station, Juliet tells Lassiter that it's time for her to take the lead on a case. Lassiter decides to give her an easy one her first time out – a couple of kids came in to complain about their teacher. Despite it being such a low priority case, Juliet decides to give it her all.
When Shawn and Gus arrive at the school to investigate, Shockley and Goddard have their cover story worked out for them already. They are going to be guest lecturers on paranormal studies. While the headmaster shows them around, Gus asks if it's possible to see records of past applicants. Shawn figures out Gus applied there when they were kids and didn't get in. While in the office, Lassiter and Juliet show up and tell them to stay away from their case. Ignoring this, Shawn and Gus decide to start by questioning the custodian, the eyes and ears of any high school, who tells them that on the night in question he found a gold pin on his rounds and put it in lost and found. They find the pin, which has an integral sign on it, and figure their guy must be a math teacher. In the teacher's lounge, they learn that the calculus teacher is Professor Hahn who is also in a carpool, which Shawn and Gus worm their way into. On the ride home, they confirm that not only did Hahn stay late at school that night, he also has a deep voice.