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

Emily is forced to deal with another devastating loss. However, her grief soon transforms into drive when she realises Rex Wolfe was only the tip of the iceberg.