In tracking down the origin of a deadly strain of tuberculosis threatening Americans, Agent Ryan Booth must go undercover and infiltrate a white supremacist organization; an assignment that threatens the life of another member of the team.

Lives are in danger as the team protects Shelby when she reunites with someone from her past, resulting in deadly consequences.

The team is in Ireland, and when they finally come face-to-face with Conor Devlin, not everyone comes out alive. And Alex makes a life-changing decision about her future.