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.

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.

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.

The FBI closes in on the person who had chosen the victims of the Fentanyl Killer. Emily is once again, confronted by evil touching her family. Nick & Alice try to resolve the problems they have been suffering, but Nick is going to make a horrifying discovery.

Emily hits a dead end. Despite this, she follows the remaining shreds of evidence to a wrenching revelation!