The episode begins with three students at three different locations sniffing a particular powder. We then see that they are appearing for their SATs. Cut to the empty library, where a student is seen sitting at a table with his head down; he is dead and there is blood all over his bag. The team arrives at the scene. Mac points at an object sticking out of his skull. He wonders why the boy in the lib on a Saturday and Don is tells him that the SATs were held this morning. Maybe he was studying late night and got locked in. Then how come the parents didn’t report him missing? Don finds the bloodied murder weapon lying under a table. ..