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.

Stunned by new revelations from her past, Emily intensifies her search for the truth. Tensions mount at the FBI as Nick and Julianne race to profile the Federal Annex terrorist.

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.

While investigating the home of the most recent Fentanyl Killer victim, Emily obtains a critical piece of evidence. Meanwhile, Nick's work with a high-profile prisoner turns deadly.

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.