Legendary Special Agent Leroy Jethro Gibbs (Mark Harmon) unexpectedly retires and is replaced by former FBI agent Alden Parker (Gary Cole). Parker is instantly put to the test as the team takes on a series of life-and-death cases. A bioterror attack exposes Jimmy (Brian Dietzen) and Kasie (Diona Reasonover) to a deadly toxin. McGee’s (Sean Murray) mother-in-law is targeted by a killer. Vance’s (Rocky Carroll) daughter is kidnapped by a cartel. Torres (Wilmer Valderrama) confronts danger and an old love from his undercover past. New agent Jessica Knight (Katrina Law) risks her life to investigate a true crime podcast. To top it off Dr Ducky Mallard (David McCallum) makes a surprise return.