Nash and Joe are on the trail of a renowned assassin who has come to San Francisco to kill FBI special agent David Katz. Lisa Bridges returns from Paris and announces she's engaged to marry a famous French chef named Henri, but there's a problem; Nash and Lisa's divorce was never finalized. The new S.I.U. headquarters is introduced.

Nash becomes the objective of mercenaries controlled by a Singapore billionaire and his American counterpart, locked in battle to capture each other's most prized possessions. Bettina wants Joe and Evan to investigate his fiancée's alleged affair.