NCIS is called to investigate when a woman is seen fleeing the scene of her husband's murder. Also, Roberta Deeks comes into town to meet Rosa, and Sam looks for another aide for his father.

When a Marine falls ill during a training mission due to an attack by a genetic weapon, the NCIS must track down the person responsible for unleashing it. Also, Deeks struggles with balancing work and home life when Rosa comes down with the flu.