When a Russian biochemist is assassinated for trying to defect with his highly sensitive biotoxins research, the Fly Team springs into action to protect his daughter, whose father's last wish was that she get his research to a trusted American microbiologist. Meanwhile, Mitchell stays behind to help Vo during her recovery, and Booth clashes with Smitty when he finds out she could jeopardize his promotion.

The Fly Team leads an international manhunt when an American woman and her new husband flee from Baltimore to Istanbul with her young son after a heinous murder. Also, Vo partners up with Special Agent Riley Quinn, who was not only sent to Budapest to work her first big case alongside The Fly Team but to also clandestinely investigate a member of the team.