The body of the son of a retired Colonel-turned-preacher is found and the team have their suspicions that he may be the victim of a hate crime. Meanwhile, Gibbs gets a holiday visit from his father.

The NCIS team searches for answers when the current husband of both Gibbs's and Fornell's ex-wife is suspiciously kidnapped.

After a mysterious illness strikes children from military families, Gibbs and the team investigate the cause. Meanwhile, Abby and Jimmy partner with the Naval Medical Research Center to determine the strain of illness, all in hopes of delivering a cure before the holidays. Also, Director Vance struggles with forgiveness as his estranged father-in-law makes a surprise visit to his home.

While investigating the death of an intruder at Quantico, Jimmy and Kasie are exposed to a deadly biotoxin; the NCIS team calls on Dr. Carol Wilson for help as they race to find the antidote; Torres tries to distract Jimmy's daughter.

NCIS investigates the fatal poisoning of one of Kasie's forensic scientists; McGee is questioned by the Pentagon regarding the contents of his book.