When the star witness in the case against Greg Csonka, the man responsible for the death of Wes' former partner, is beaten to death in a Budapest prison before he can testify, the Fly Team attempts to salvage the case to secure Csonka's conviction. As they dive back into the investigation, Mitchell is forced to confront the pain of losing his partner. Meanwhile, Wes assists Booth with preparing for his promotion interviews.

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.