When a passenger train is hijacked and rerouted while at high speed with an unarmed OA and Gemma on board, the team races to wrest control away from the unhinged perpetrators and prevent a catastrophe.

When an undercover FBI agent is killed in the field, the team makes the unnerving discovery that the identities of multiple undercover agents have been compromised, including Maggie who has been actively working to infiltrate an eco-terrorist group. Meanwhile, the team enlists the help of Special Agent Dani Rhodes, whose cover was also blown, to not only save their own but to aid in uncovering who was behind the leak.