Eric and Horatio arrive at CSI HQ barely in time to prevent toxic gasses slaughtering their colleagues. Tragically, it's too late for Jesse, who hurt his head while falling. It's clearly the work of serial killer professor Bob Starling, but also destroyed most evidence against him. Several trails or followed, laid by him, causing confusion about his accomplice(s), notably the part played by ruthless opportunist Melissa Walls and campus janitor Keith Garwood. Starling's plan includes computer-controlled weapons and daring escape.