When a passenger train collides with a freight train, the FBI is called in to help rescue survivors and to investigate the cause of the crash. Complicating the situation, the freight train was carrying a large amount of toxic chemicals and there was no apparent mechanical failure that led to the crash, suggesting that sabotage and terrorism may have been the motive. David and Colby work with Charlie to map routes to the survivors buried deep inside the wreckage, while Don, Nikki and Amita follow up on what caused the crash. Amita breaks the case wide open when she discovers the technician responsible for switching the tracks had put in the order too late. Don questions the technician, and learns that he had simply fallen asleep, but also that the freight train should have been able to stop in time, regardless of the mistake. It turns out that the owner of the freight company had been under reporting the weights of his shipments to save money, and that extra weight had caused the accident.

Meanwhile, back at the crash site, despite losing some of the crash victims, the team is able to pull off several miraculous rescues.