With Tired Eyes, Tired Minds, Tired Souls, We Slept(Season 3, Episode 16)

Jimmy enters the high school. He's visibly shaky and he scans the hallway, seeing one the punks who beat him up at the benefit concert. The punk forcefully bumps Jimmy as he walks by. Jimmy turns, pulls out a pistol and fires a shot, but instead of hitting his intended target he's fired through the glass library door, right where Peyton and Brooke are standing.

The principal immediately announces a lock down as various students run for their lives. Brooke ends up outside alone.  Haley shelters herself in the tutor room along with Mouth, Hey! It's Rachel, Skillz, Abby(new character!)and this other kid named Marcus. Brooke is put on a bus by Whitey with some other kids and sent away. Nathan rushes toward the school to save his beloved. Lucas tries to stop him, but quickly realizes that "holy crap, Peyton's in there too," and they both decide to play hero. They're so manly!

Lucas finds a wounded Peyton hiding in the library,  She initially thinks she's been cut by broken glass, but it's much worse. She's been shot, and she's  growing weaker and weaker from profuse blood loss.

Brooke confronts a reporter that is obviously trying to make a name for herself out of this whole thing. The reporter accuses Brooke herself of shunning Jimmy, and others like him, and she's right. A distraught mother asks Brooke about her daughter's whereabouts, and Brooke has never heard of this girl, even though the mother insists the two of them are friends. Brooke is very overwhelmed by this, and makes it her duty to befriend the girl for real.

Nathan discovers confused Mouth wandering around, and they gain entry to the tutor room by sliding Nathan's identification under the door.  But there's a problem: Jimmy's been inside with Haley and the others, and he reveals himself to be the gunman.  Things get really really touchy from here on out, with lots of crying, and not just from Haley and Rachel. The biggest part of it comes from, who is very upset is former friend could do such  a thing.

Jimmy tells his terrified hostages about how he once attempted suicide, and when he returned to school after a lengthy hospital stay, no one had even noticed he was gone(not even Mouth). Mouth insists that he tried to do things with Jimmy, but Jimmy was distant and didn't want to do things. The kid named Marcus freaks out and attempts to fight Jimmy, but Skillz punches him out to save him from having his dumb brains blown out.

Abby becomes ill because she's diabetic and has no insulin with her. Haley and everyone else implore Jimmy to let her leave, and he relents. For a moment he looks like he's going to shoot her as she runs off, but he does not. Whew! This is enough of a distraction to allow Nathan to text his father, who is outside the school with Keith.

Jimmy realizes his time is probably, and he walks out of the room. The kids sit there stunned. He discovers Lucas attempting to carry a dying Peyton out of the building. BUT WAIT! Keith appears, and steps in harm's way.

Adventures Of Keith: Keith attempts to console Jimmy by telling him of his own tragic past, including that time he bought a gun to kill Dan and himself. Despite his very best efforts, Jimmy is too far gone for this to be any use and kills himself. Keith mourns Jimmy, and Dan is there to share his grief. But then Dan takes Jimmy's pistol and shoots Keith dead. HOLY FUCKING SHIT! What else do you say after something like that?

This episode was no doubt very controversial when it first aired, and it still is very effective(and unfortunately still relevant) eight years later. It also introduced a much darker tone to the series that carries over into other seasons. Now, join me in a moment of silence for Keith, a decent man who got screwed over again and again, finally found happiness, and then was murdered in cold blood.