When a runner drops dead in the middle of a marathon and the cause seems to be carbon monoxide, Mac and Stella can't reconcile how someone would be poisoned in the middle of Central Park. With thousands of suspects and no witnesses, the CSIs fight to collect evidence while spectators and marathon runners contaminate their crime scene. Meanwhile, a high-end vodka's ice-themed promotional launch party turns deadly when a model is stabbed, leaving Danny and Lindsay racing to collect vital evidence before it melts.