Emily Byrne struggles to make sense of her time in captivity and her tumultuous past. Meanwhile, a deadly terrorist attack rocks the heart of Boston.

Reeling from a shocking loss, Emily returns to the FBI to get answers. Meanwhile, Nick and Julianne fear the terrorist may be ramping up for his next attack.

Emily and Cal's investigation into the Fentanyl Killer points them toward some dangerous and highly skilled suspects. Elsewhere, Nick's manhunt for the Federal Annex attacker heats up.

Emily and Cal travel to Moldova to track down the Fentanyl Killer - a task that proves to be more dangerous than anticipated. Meanwhile, Nick is given an order that challenges his moral code.

Emily and Cal venture off the grid as they track Rex Wolfe deep into lawless territory. Back in the States, Nick struggles to swallow a massive lie.